My truck actually came with ATs (it's a used truck). It tows great, but I question whether my truck would be better off with P tires next time. I don't tow a super heavy trailer, and a bit nicer ride quality and better gas mileage would be nice depending on what the tradeoff might be in towing quality.
My previous truck had P tires on it and did not tow nearly as well, but I think that was more a function of the truck than the tires. It was a 2006 Tundra and was a little less truck than I needed. It was pretty floaty, but that may be more due to the truck than the tires.
Matt