"perfect", will depend on what it's being used for. For instance, a "target" bow, can be heavy, long, ugly, loud and many other things a hunter might shudder at.

I'll guess that we're talking about a hunting bow. For me, it's a combination of length vs weight. Shorter is never better, unless you are shooting from a very cramped area or the bow gets too heavy to be comfortable. Minimum shootable ATA will have a lot to do with draw length. Optimum ATA will be related to anchor points, especially if you don't use a peep. Bottom line - it's different for people. No one ATA works for everyone.

I really dislike the parallel limb design bows. Besides being ugly, the longer ATA ones have such heavy risers. There are days when I walk quite a few miles with my bow and the heavier ones are simply more of a pain in the butt. Walk a day with a long parallel limbed compound and then a day with a longbow, and the extremes can be felt - literally.

Bottom line - in a hunting compound, I want a longer ATA with a short riser, 8" brace or more, shorter riser, a cam that gives me a smooth draw cycle and straight nock travel. Unfortunately, I'm not even sure they make such a compound anymore. Bows are being designed to shoot an arrow faster than the other guy's bow and to have absolutely no forward recoil on the shot. Both of which I care nothing about.