Get the Nexus 4 in a week. You can then try straight talk on AT&T ($45) and T-Mobile Prepaid ($30) with the same phone. When you figure out which works best for you, stick with it. Nothing is better than personal experience.
The Commandments of Android
1) Open RAM is wasted RAM - Don't use Task Killers
2) Cheap devices are cheap for a reason. Don't expect high end performance.
3) Boot Loop = Wipe.
4) There are no viruses for android.