Switching from iPhone. Advice?

After using a friends Nexus 7 recently I've been interested in switching over to Android. I think the next Nexus device would be best, but my at&t contract ends this September and I don't want to be without a smartphone for 2+ months. What do I do in the interim? I've considered switching over to T-mobile for the unlimited plan. Though, I live in dallas which has really good At&t coverage but shitty t-mobile. That might change with it's rollout of LTE, any ideas?

Do you think an iPhone under at&t would be a safer bet to make for the next two years until the carrier/phone situation becomes a little bit clearer?