Future readers of this thread:
If you are considering which one of these based on how much money you will spend, then you´re looking at the wrong factor. They are different sizes of armour. If you wear a size xlarge T-shirt you´re not going to buy a size medium. Same thing with ATA and AM. AM is for large guys, ATA is for smaller guys.
Yes, you can trim an AM to be smaller, and you can shim ATA to be bigger, but you get the analog I think.