Hi Beach View,
I ride size 14 (Flow) boots and got in a great day on the SE's this week. I am very sympethitic to our friend above with size 15 boots. While there are some 15 boots that do work well, there are others (especially older boots) that do not. Size 14 and down in modern boots all fit easily.
As for the SE / AT question, this is entirely preference. The toe cap does pull you back amazingly well. I kick in as usual and then take a couple of clicks just after kick in. There will be riders who don't want toe cap and i completely get that.