The PS4 uses a Sata II controller for it's HDD so it really won't take advantage of SATA 6Gb/s it's basically limited in that regard. So SSD's will be limited as well due to the limited speed that Sata II has.
Of course going from the stock 500GB to a 1TB is a modest upgrade and since every PS4 game installs entirely to the HDD, capacity might more important speed.
I recommend the Samsung Spinpoint M9T. It is a 9.5mm 2TB HDD that works in the PS4. It is the current largest capacity 9.5mm drive available. The PS4 drive cage itself doesn't support drives larger than 9.5mm so this is your best bet in terms of reasonable pricing and storage capacity.
You can either buy the bare drive itself which costs more
http://www.amazon.com/dp/B00MI19WXK/?tag=neogaf0e-20
Or you can buy this and remove the HDD from it's enclosure -
http://www.amazon.com/dp/B00FRHTSK4/?tag=neogaf0e-20 and get the exact same thing for less
Also if you are careful enough, You can preserve the enclosure for the Slim Backup Plus and reuse the default 500GB PS4 drive as removable storage.
The Spinpoint M9T is $80 so it's $20 more then that Hitachi drive, but again it's also twice the capacity.