I have T-Mobile and have used 5 of their BB dating back to their 7730, but here's a few things to consider when purchasing a BB from any carrier. I am not trying to get you to switch to T-Mobile (or the 7xxx series), but this has been my experience.
I would trial both and see which one you prefer. Here's a few things to observe if you decide to test drive both devices. Both devices have the email notification LED.
1) Signal-which one stays the strongest no matter where you use it? I had to deal with this problem from day 1 and had so many times with 2 7730's it wasn't funny. Gave up and changed over to the 7100 series and had only one issue which required a replacement.
Couldn't travel with the 7730's. Took the 7100t to camp last year and no problem, but for some reason still unknown, six months later the radio died. It turned on but never got signal.
2) Battery Life-same issue as above. Got 1 day (if that) from my 7730's. I can get 4 days heavy use out of the 7100's, with an extended battery. This is with the BB not connected to the PC.
3) Durability-equal. I dropped all (6) of my BB's and all of them kept working like a charm. The keyboard durability is usually a user preference. I would test drive both in this situation.
I had no keypad problems on any of mine. Had a power button problem with one of my 7100t's but it was replaced with no questions asked (same phone that had the signal problem).
Hope this helps you pick out the BB that fits your needs and performance requirements. But beware: You WILL become addicted to it LOL