I want to try Android on a phone.

Currently own the iPhone 5, which I like, but I'm becoming more and more curious about Android as my daily driver. I owned a Nexus 7 in the past and liked it. I want to try out Android on a phone for ~$100 if possible.

What Android phone would you suggest for ~$100 (new or used, no contract) that would work on AT&T and give me a good representation of what Android is like? LTE not required, but a plus. Newest version of Android possible. I want to swap SIMs from my iPhone 5 (with an adapter).

I also just bought a Lumia 520 to try out WP8...AT&T GoPhone, $100 out the door, no contract required. Just swap SIMs.

Thoughts?