I've been using Linux desktops since the leading desktop front-end was Bash. Things have changed in those 25 years. Today, the best Linux desktop is the latest version of Linux Mint: Linux Mint 18 Sarah with the Cinnamon 3.0 interface.
Indeed, from where I sit, it's not only the best Linux desktop, it's the best desktop operating system -- period.
As such, Mint uses the Linux 4.4 kernel. On top of that it uses the X.org 1.18.3 windowing system. While Mint's default desktop is Cinnamon, like I said earlier, you, not some company, get to choose your desktop. MATE, the GNOME 2.x clone, is already supported. Other desktops, such as KDE, LXDE, and Xfce, will be available soon.
Despite these changes, Mint still runs on old computers you have sitting in your garage. You only need 512MBs of RAM to run it, although 1GB is recommended. You can fit Mint on a 10GB hard-drive, although 20GB is recommended. As for a display you can run it on 1024×768 resolution or even lower if you don't mind using the ALT key to drag windows with the mouse.
There have been some changes in what Mint can support. The 64-bit ISO image can boot with BIOS or UEFI, but the 32-bit version will only work with BIOS. Mint highly recommends running the 64-bit version on any modern -- late 90s and up -- computers.
I ran Mint 18 on a system with hardware specs that were overkill for it: My work desktop. This is an older Dell XPS 8300. It has a 3.4GHz quad-core Intel Core i7 processor, 8GBs of RAM, and an AMD/ATI Radeon HD 5770 graphic card. Mint 18 ran great on it.
Mint 18 also ran smoothly on my 2011 Lenovo ThinkPad T520 laptop. This notebook computer comes with a 2.5GHz Intel Core i5 processor, 4GBs of RAM, a 500GB hard drive and an integrated Intel HD Graphics 3000 processor.
The new Mint also features new software. For the longest time, Cinnamon continued to use GTK3-based GNOME desktop apps. In practice this mean Mint's developers used older program packages that had been patched to look like Cinnamon apps. The Mint team has gotten tired of this thankless task.
Xreader which sprang from MATE's Atril and is the new default document and PDF reader.
Xplayer which is built from Totem. This is Mint's new default media player for music and videos.
If you really want to use the older GNOME applications, you can. I wouldn't. Except for the names, the only thing you'll notice about these new apps is they look and work better.
Mint also features up-to-date versions of popular Linux applications. These include Firefox 47 for web browsing; Gimp 2.8.16 for graphics editing; LibreOffice 3.12 for the office-suite, and Thunderbird 38.7.2 for the e-mail client.
Of course, if you'd prefer something else, Mint makes it easy to switch it up. For example, I immediately replaced Thunderbird with Evolution 18.104.22.168.
Mint's system Update Manager has also received a nice face-lift. With it you can now easily choose between:
Update the system with stable versions of software
Update the system with stable versions of software as above, but show whether the user would like to install additional updates which could lead to instability issues
Update everything, and if something breaks, then you better know how to fix it!
You may notice that update to an entirely new operating system, which you may not want, isn't listed.
Besides, once you get used to Mint, which looks and works a lot like Windows XP, you may not want to move to a new operating system. I haven't, and I use almost every desktop OS on the planet.