In terms of quality, and this is purely my opinion - but you're either going with an iPhone 5 or a Lumia 920.
That's just my opinion. Frankly, I think the iPhone 4 is a better product than the 5, but whatever. I'm just saying for build and material quality Apple and Nokia are the two main companies out there to look at.
HTC has it's followers but the phones just don't feel right to me. They're just a slight step down from Apple and Nokia. Samsung then follows - a good distance behind with it's Galaxy series.
It's all opinion. Go to a store, pick one up and try it out. I love the way the Lumia 920 feels in hand. I've had iPhones for years - and I always noticed them in pocket. I pat my pocket constantly now because I can't tell if my phone is in there and it's not only heavier but it's substantially larger than my iPhone 4 was.
The 920 just has fantastic ergonomics. Again, opinion. Someone with smaller hands may not feel the same way, obviously. My wife is nowhere near my size and she also loves her 920 - coming from an iPhone, as well.
If you get it from AT&T you've got 14 days to try it and return it if you don't like it.
I personally felt like Apple really didn't hit the target with the iPhone 5 so I, and my family, switched to the 920. We all love it. I have no regrets leaving iOS at all. In fact, I'm quite happy to be switched to WP8. There are some differences that got my attention at first, but overall and over time I much prefer WP8 at this point.
The last update to iOS really sealed the deal, too.
Just my 2 cents.