I can't say that ATS has the best carne asada I've had in Phoenix, but the atmosphere and the patio make for a great evening. What's more, the bean and cheese burrito is pretty fantastic. I've also had their breakfast burrito a few times; you might want to ask for an extra side of salsa.
The best part of ATS -- the staff is friendly and chatty. I was glad they placed a tip jar near the register.
If you've ever visited Houston, you'll understand what I mean when I compare happy hour at ATS to happy hour at Mission Burrito. The food couldn't be more different, but that atmosphere is quaint and enjoyable.