I don't know that I have a least favorite breed, I'm more about temperment. I do NOT want a hot, spooky horse for myself. For that reason I would probably shy away from Arabs and Saddlebreds, because most of those that I've met personally seem to be that way.
However, I wouldn't necessarily shy away from TBs because one of the first 2 horses I owned (bought 2 within weeks of each other) was an OTTB, and he was a wonderful horse. Sane, fun to ride, not spooky at all.
The other first horse I bought was an Appy/Draft cross, and he was terrible. Big, scary bolter who was also really stubborn and pushy. Every time we cured one bad habit with him, he thought up a new one. I would probably not have another Appy just because that experience was so negative for me. He did have a really nice tail though lol.
My favorites are QH and Paints, and I admit that fancy it's color that tends to catch my eye (that's how I ended up with the crazy black and white leopard appy!), but if I was in the market and someone had a quiet, sane horse of almost any breed, I'd give it a look.
Probably wouldn't go gaited at this point because my girls are just getting into showing 4H, and gaited horses tend to get judged very poorly in the pleasure classes at 4H shows (at least in this area)