I personally feel that the armor quality is better with AP than with the ATA suit. The helmet issues Panda brings up are true, but overall i feel the AP armor is better (i own both AP and ATA). But, the ATA was an easier build.
However, 1 thing that biases my view is i am pretty skinny (5'11" and 155lbs) so the AP armor fits me like a glove. I had to trim down the ATA suit a TON to get it to fit. I could easily have fit it if i was more like 200lbs.