If you're considering buying a Retina MacBook Pro (13 or 15-inch) or upgrading the SSD in one, you should check out the OWC Aura Pro the only compatible blade on the market. Not only is the Aura Pro 480GB SSD blazing fast, but it costs $200 less than Apple's offering -- and you get to keep the original Apple module as a backup.
When you configure a new rMBP from Apple, upgrading to the 512GB option will cost an extra $800:
Instead, stick with the stock 128GB Apple SSD and opt for the Aura Pro 480GB SSD ($580) from OWC instead. Although 480 looks like 32GB less than 512, looks can be deceiving. The Aura Pro actually has 512GB of flash on board, but OWC sets aside 32GB for real-time data redundancy and error correction, leaving 480GB available.
Then there's the speed issue.
Apple uses a Samsung processor in its rMBP SSD, OWC uses SandForce. MacObserver benchmarked the OWC against the stock Apple SSD and determined that "sustained reads and writes on the OWC Aura Pro beat the stock Apple SSD by over 100 MB/s" and that "the Aura Pro was also much faster and random operations than the Apple SSD."
MacObserver's results back up OWC's benchmarks, which show that the Apple SSD's write speeds are significantly slower:
...than the OWC SSD write speeds:
The icing on the cake is that when you upgrade your rMBP with a SSD from OWC you get to keep the original as a backup. Because Apple uses a proprietary SSD module, so you'll have wait for OWC to begin shipping its sleek Envoy Pro external enclosure to use the stock SSD as an external drive.
Installing the Aura Pro SSD is simple. OWC includes the two screwdrivers that you need to complete the process. Until the Envoy Pro enclosure begins shipping later this year, I recommend making a Time Machine backup of your data and then transferring that onto the new SSD. Upon first boot with the new SSD, you need to perform a PRAM reset by holding down the Command, Option, P, and R keys after pressing the power button (but before you hear the startup chime.) After the computer restarts (and you hear the startup chime a second time) let go of the keys and let the MacBook Pro boot normally.
Although there's a little bit of labor involved, the OWC Aura Pro 480GB SSD is faster and cheaper than the Apple option -- what's not to love?