Venues I have been to: UCLA (rose bowl), USC, SDSU, TCU, Nebraska, Arizona...
Nebraska fans were the nicest. No one was rude or mean in any way. Veyr helpful.
UCLA/USC were about the same. Neither said much and no one was rude, but were not nice either. Just minded their own business.
TCU fans were generally ok, but a few were not great. But it was not a terrible experience.
SDSU, fans didn't say much, but I don't much care for the moking of the church with them dressing up as missionaries.
Arizona...been to several games in Tuscon, both as a BYU fan and also went to the ASU-U of A rivalry game. These fans are a special kind of trash. Its the only place I have been where I have been cussed at while wearking BYU gear. But I also went to the rivalry game and sat near some ASU fans. What i got as a BYU fan was miled compared to what the ASU Fans got. It was bad.
The only thing I will say, was I went to the game last year in Tuscon and sat in dsabled seating (good friend of mine is in a wheelchair) above the student secrtion, wore BYU gear, and never had a negative interraction with any U of A fan at that game.