they are both easy to root (on android 4.4, android 5.1 is only recently rootable but its hit or miss) but both have locked bootloaders so that's as far as you can go at this point.
they are pretty hard to find now but if you want LTE and an unlockable bootloader you want the P905 model.
otherwise if you can do without the LTE the wifi models are unlockable as well.
Also if you do get one of the carrier versions make sure its SIM unlocked unless you use AT&T service.
the Verizon model is innately unlocked but I believe the AT&T model is locked to AT&T by default.
for reference:
Bootloader Unlockable and rootable:
- SM-P900 - Wifi (Exynos Processor)
- SM-P901 - 3g and wifi (Exynos Processor)
- SMP905 - LTE and wifi (Snapdragon Processor)
Rootable but not bootloader unlockable yet:
- SM-P905V - Verizon LTE and Wifi (Snapdragon Processor, locked bootloader)
- SM-P907A - AT&T LTE and Wifi (Snapdragon Processor, Locked bootloader, locked SIM by default.)
The two processors are pretty close, the Snapdragon has a better GPU, the Exynos does a bit better multi threading.
the big gain everyone hoped for with the snapdragon was quick charge but I have a snapdragon version (P905V) and havent had any luck getting quick chargers to recognize it as a quick charge device for what its worth.
Lastly, I'm not sure if its a big deal to anyone but note the P905V does not get SMS messages when using a GSM provider (If you use Verizon it should be fine)
I don't have the P907A but since it is GSM I don't think it would have an issue.