Definitely try on every brand you can. I love a lot of designs by Justin and Tony Lama, but my feet completely disagree with their shape. Ariats are the only boots to fit my little, narrow feet well and be comfortable.
I've noticed that some Ariats, also, are wonderful and last forever, and some don't. Mine are 3 years old and are shot. I blame wearing them so much in the snow, which is my fault. However, this pair is not deferring me from buying from Ariat. In fact, I'm trying to decide between 3 pairs to replace them.
Oh, also, if you have smaller feet and don't mind shorter uppers, check out the kid's section; they're half the price. I was trying on boots last week and the square toes I was interested in run big. I usually wear a 7 in boots, but I needed a 6.5 in these two pairs but they didn't have any. The lady suggested a 4 in kids. I found the kids' version of one pair I liked that fit fabulously, I just didn't like the shorter uppers.