I've been to both.

Aviator- older airplanes, more formal college style learning environment, slower training pace

ATP- newer airplanes, faster training pace

If you like learning in a formal classroom environment and training at a more steady pace, I'd look more into Aviator. If you're fine studying mostly on your own with the occasional questions for your CFI, and training at an intensive pace, I'd tend towards ATP.

Also, I don't know where you are based, but ATP obviously gives you better choice on locations. Aviator is out in the boonies and you'll need a car if you want to do anything other than hang out at the airport or their housing.