I've started going to at least one away game a year two years ago, so don't have a lot to draw from. I will say that the Notre Dame fans two years ago (when we were favored to win before the game) were VERY cordial and welcoming. A lot of them went out of their way to welcome us and make sure we could find what we were looking for.
Last year, the Texas fans we interacted with were nice enough, but not exactly friendly. They weren't rude - even after we destroyed them on the field, but they didn't go out of their way to be nice, either.
I've been to SDSU a couple of times, but it always felt like there were more BYU fans there than SDSU fans. Their fans just kind of knew they would lose to us. Some were obnoxious, but most were fine.
I'll be going to Nebraska and Michigan this year. I fully expect (and hope) that the Nebraska fans will be cordial, from everything I've heard. Haven't heard anything about Michigan fans, but since they don't have the Nebraska or Notre Dame reputation, I expect they'll be more like Texas fans.