Since the iPad's introduction in early 2010, it has quickly become one of the most popular platforms for reading eBooks, simply due to the variety of content providers which have written applications for the device.
However, the average iPad user may not be aware of features or limitations in the various ebook reader apps available on the App Store, so I'm going to try to boil this down so that you can make the appropriate choices which best fit your reading lifestyle.
As of June of 2010, Apple has imposed restrictions on its App Store as to how ebook reader applications can distribute content.
As a result of these changes, many of the applications listed in this article are no longer capable of buying content directly from the application, and can only act in a "receiver" mode where content is purchased outside the application (such as by using the iPad's built-in Safari browser or browsing using your personal computer) and then synchronized to the ebook reader program.
While this is not by far an exhaustive list of ebook reader apps for the iPad, these are the ones that made our short list.
By virtue of being Apple's preferred book-reading platform, iBooks has quickly become one of the most popular ebook reading applications for iOS. iBooks runs native on the iPad, iPhone and iPod Touch, giving it some of the largest consumer reaches of any ebook reading platform available.
While there is no doubting iBooks' success in terms of its widespread use, compared to all of all the other reader applications we've looked at, it actually has a lot of functional deficiencies.
Apple originally designed iBooks to behave and act like a real book, and focused more on the aesthetics and UI than actual App functionality.
One of the main benefits of iBooks is that unlike the two other major ebook reading applications, Kindle for iPad and Barnes & Noble e-Reader, iBooks supports syncing of DRM-free EPUB and PDF content directly to the iPad thru iTunes.
This is an excellent feature, but essentially locks the user down to using iTunes as the primary data transfer mechanism and thus requires a host PC or Macintosh in order to maintain the library.
Additionally, EPUB and PDF content synced into iBooks' library is not accessible by other e-Reader applications. Generally speaking, every e-Reader app for iPad maintains its own separate database, and is not compatible with each other.
Unfortunately, iBooks doesn't scale very well as the size of your EPUB library increases. While iBooks is perfectly fine for a few dozen or perhaps a hundred or so books purchased from the iBooks Store or synced into iTunes, it is extremely unwieldy once you approach 300+ titles loaded into the database.
In casual testing we uploaded over 1,000 full-length EPUB novels to iTunes which we synced to the iPad. We encountered a number of connectivity/timeout issues with the iBooks sync on Windows, plus we discovered that iBooks performs badly when browsing in "Bookshelf" mode when many titles have been loaded into the application.
We found that the less aesthetically-pleasing "list" mode actually works better for browsing a large content library. Although the third, fourth and fifth-generation iPads are much faster than the original iPad and the iPad 2, caching that many titles into the database still causes the app to perform very slowly, so I wouldn't recommend using iBooks for storing your entire personal library in EPUB format.
While Apple has made a number of performance improvements to iBooks in the four years since its introduction I'd still say that the iBooks software isn't as sprightly as the others on this list.
The aesthetic focus of iBooks is also in my opinion one of its most serious weaknesses. Much time has been spent by Apple's developers on how the app looks in terms of eye-candy and very little time was spent on how well the application works for actual text reading.
The current version of iBooks has 3 color schemes (black on white, sepia, and inverted white on black) and seven font variations.
Although iBooks got a major overhaul for iOS 7 by elimination of skeumorphism from the UX, there is still no way to set iBooks to maximize the most use of screen real estate and adjust margins. Four years after release this is a huge peeve.
One thing that iBooks does that many of the apps on this list cannot do is have embedded interactive content. Most if not all of these are created using Apple's iBooks authoring tool that is specific to Apple's platform.
Many of these books are educational texts, and I haven't seen much in terms of fiction and non-fiction titles or even magazines that make use of these features. As of this writing the "Made for iBooks, Our Recommendations" section is pretty slim picking, a whole 55 titles total.
This isn't to say there aren't a lot of iBooks Author-optimized titles in their catalog if you include the educational texts, but as far as showcase works, obviously not a whole lot.
Still, by far iBooks' best asset is the iBooks Store, which has a familiar interface similar to the App Store. It's very easy to search for content and you can get free reading samples for just about every book in the store before you decide to purchase.
Because it is Apple's official eBook reading application, it is also now the only one which offers an integrated bookstore.
The Kindle application is something of the red-headed stepchild for ebook reading. For Apple and the iPad platform, it remains something of a necessity, this despite Apple's desire to control as much content as possible, as Amazon still has the widest array of paid ebook content in existence, with well over one million titles in inventory.
However, from a feature perspective, the Kindle software is pretty weak when compared to its hardware counterpart. You can't import other file formats into it (such as PDFs or .MOBI files) and it only works with titles you've already purchased in the Kindle store.
Obviously, if you've made a substantial investment in Kindle content in the past, you've got access to your entire paid library with this app. Over the years I've evaluated several Kindles and purchased content in the store, and all my books appeared in the application instantly, this despite not owning an actual Kindle.
Kindle has an interesting feature called "X-Ray" which if enabled for the title by the publisher, allows you to learn more about the books that you are reading, translate the text in your Kindle book, zoom in on images, and view book or periodical recommendations.
There is also a feature called "Book Extras" which uses Amazon's Shelfari social networking service. However, this only works if there is a Shelfari entry for the book and it has activity on it.
Kindle also makes better use of screen real estate than iBooks does. There are three margin and three spacing presets, and two pagination types, columns or no columns. Like iTunes there are three color schemes, white, black and sepia, and there are seven selectable screen fonts, including the one set by the publisher.
Of all the paid content readers, one of the best is probably the Barnes & Noble NOOK application.
About the only negative thing I can say about it is that like Kindle for iPad, the application is limited to content already purchased on the B&N website. Of course, if you have a NOOK device, and you've invested in the Barnes & Noble ecosystem, this is the app for you.
Other than that flaw, I love this app. The reading experience is far superior to that of the Kindle application, as it has six built-in themes for different colors of text and background, a theme editor that allows you to make your own text and background color combinations, and has six of the best reading fonts I've seen in any of the apps I looked at, especially when viewed in the "Gray" theme that almost has me convinced I'm looking at e-Ink and not an LCD.
Margins can be adjusted directly from page view to make maximum use of the screen if you'd like.
The only thing that would make the B&N application perfect is that if you had the ability to import your own EPUB and Adobe DRM content, which unlike their (arguably not long for this world) Android-based NOOK reader device, you can't do yet.
Kobo Reader for iPad is something of a dark horse when compared to the three major paid content eReader apps, but it's extremely polished and very well-designed.
Kobo's main benefit is that it supports many different computing and smartphone platforms, so you can have all of your content available with you wherever you go.
Like Kindle and B&N, your content is stored in Kobobooks.com's cloud, so it doesn't matter if you are using Kobo for iPad, iPhone, Android, Windows device or Mac.
Kobo also produces its own brand of e-Ink reader, which you can purchase from their website. It looks like it has some very compelling features, which includes the ability to Bluetooth sync Kobo books from your smartphone device.
Owners of the now discontinued SONY ebook reader and book store will find solace in Kobo in that their libraries and purchases will be migrated over. So if you've invested in SONY books, you can now read them on your iPad.
The Kobo reader application is one of the nicest looking on the iPad platform. You have nine scalable fonts to choose from plus a White-on-Black "Night Reading" mode as well as a Sepia tone color scheme.
Margin adjustment is not supported, but otherwise this is an excellent application.
The latest version of Kobo has a social networking feature that allow you to show your friends on Facebook what your current reading list is. Other features include a "Stats" area for showing book reading progress as well as an "awards" area for reading that is similar to the milestone badges that are offered on Foursquare. There's also a "Beyond the Book" feature that is similar to Amazon's X-Ray and Extras features.
As it stands today, we found that pricing on major bestsellers on Kobobooks.com was comparable with the other three major paid content apps, so Kobo should be a good choice if you're the type that wants to read paid content on multiple devices.
While I would generally consider Google Play Books to be an "Also Ran" in the paid content ebook reader software category when compared with Amazon or Barnes & Noble's applications, Google Play Books does fill a very interesting niche, and that is free access to the massive collection of millions of scanned volumes from its Google Books project.
Because many of the volumes in Google's vast inventory are scanned from classic literature, the application has the ability to view content in its original scanned form, including the illustrations and the original typesetting.
This is both a feature and a weakness, as sometimes you will notice that as a result of the scanning of a particular work of literature, the text and or illustrations may appear warped due to the way the paper may have moved through the scanner device.
However, a lot of the more important volumes were also OCRed, so you can read many of these books as straight-up ebooks just as you do with the other applications featured on this list, simply by selecting "Flowing Text" instead of "Scanned Pages" from the Settings menu.
In addition to being able to switch from scanned and regular ebook mode, Google Books features a "night" mode with inverted white on black text, sepia mode, support for seven different typefaces, three types of line spacing and a wide variety of text sizes. However, margin adjustment is not currently featured in the application.
Bluefire fills a very important niche because it is currently the only application on the iPad which will allow you to borrow ebooks from your public library using the Adobe Digital Editions DRM platform, as well as paid content from other platforms which use that format, such as the (ill-fated) SONY Reader, the Barnes & Noble NOOK and also the Google Play store.
This is particularly important for those with SONY eReader devices because with the recent closure of SONY's store, Bluefire (along with Kobo) is one of the best options to get that content onto your iPad.
In addition to Adobe DRM ebooks, the reader supports side-loading of regular EPUB files.
In addition to having the key DRM content functionality, it does have a number of other compelling features, which includes adjustable text sizes, adjustable margins, justification toggle, adjustable text and background colors and eleven pre-defined themes, a huge selection of font faces, four different page turn options and the all-important "Night mode".
In addition to being able to import your own content into Bluefire, you can also access free books from Feedbooks from within the application.