iPhone 5 is released:
#10 Verizon LTE Network HUGE compared to AT&T 4G LTE
#9 AT&T tried to confuse everyone by calling their HSPA+ network 4G, when it really isn't.
#8 AT&T successfully got Apple to label the iPhone 4S as "4G" after the last update when it really isn't
#7 AT&T is going to NOT include FaceTime over Cellular for all their customers (Hint: FCC might consider this illegal and clamp down)
#6 AT&T voice quality sucks. Really tired of dropped calls.
#5 Simultaneous voice/data will be possible with 4G LTE iPhone, right not only AT&T iPhone 3G/4/4S can claim this (Hint, you will need to be in a 4G LTE area for this to work, as data goes over 700 mhz and voice over 800/1900).
#4 Stuck with AT&T years ago when they were the exclusive one
#3 Even Verizon iPhone can do international roaming - used to be only AT&T GSM phones would only support this.
#2 AT&T is usually first to charge more for features (can you say tethering)
And the #1 Reason (worth repeating): Verizon LTE Network HUGE compared to AT&T 4G LTE