I was in a similar boat, talking with both AM and ATA. I decided to commit to ATA's wait list because of the screen accuracy and ability to make it centurion grade. I'm also not that big of a guy that I would need "big guy armor." I understand it's going to be a little more work with trimming and such, but it should be worth it. AM has a great product to offer as well. Their kit comes pre-trimmed and I understand from others that it is a fairly easy build to get your suit done and functional pretty quickly.
It's all up to you and how far you want to go with your armor. Personally, I want to make my HWT as accurate as possible.