Can't offer thoughts on AT&T's prepaid, but I can share my experience with one of its MVNOs.
I switched from Tmo to Net10's AT&T micro sim since I got no indoor coverage on Tmo in my home and no complaints here. Even when traveling through rural Oregon 95% of the time I can stream youtube when I want. Tmo is faster and you get a lot more data, but all the data didn't do me any good if I couldn't get service in my home. Some people complain about MMS messaging with Net10, but I don't do that so I never crossed that bridge. Customer Service and the Forums are an absolute nightmare. You'll die a slow death waiting before anybody helps you so you are pretty much on your own. Another problem is -- at least with Net10 -- your phone deactivates if you don't set up auto pay or renew each month and it is a pain getting it reactivated. Another complaint I've seen about Net10 is that people don't get data when they travel, but as I stated above I had no problems.
I haven't seen too many post about anybody actually using a Nexus 4 on AT&T's go phone. In fact I don't think I've seen any actual first person posts (unless someone posts before I finish my post), but I've seen people post that somebody they knew or their girlfriend uses go phone with a Nexus 4 without issue.