I just bought a Moto X from AT&T off contract, and I was debating between AIO and GoPhone. As far as I can tell, AIO throttles to 8 mbps on LTE, and 4 mbps on HSPA+, and gophone doesn't throttle (you get same theoretical max speed on gophone as contract AT&T, but contract users get first priority).
The $60/2 GB plan on GoPhone ends up costing about $54.60 after CallingMart discount/code/reward, and there are no taxes/fees. So the monthly price is basically the same between the two carriers. It boils down to:
AIO: PRO-3rd month free, soft cap at 2GB (after that it throttles to 2G but you still get data)
CON-4g/LTE are always throttled
GoPhone: PRO-No throttling on 4g/LTE
CON-Hard cap at 2GB
Pretty minor differences, but they might matter to some people. I chose GoPhone just because I had to call support to port my number, and I figured AIO support would be slammed on their first day of nationwide sales. The GoPhone support was clearly outsourced, but they were fast and helpful (unlike any Verizon support experience I've ever had).