1-Hard to answer this question as I haven't been in most of the relevant venues unfortunately, but from what I've seen I'd go with Dortmund, United, Atlético, Liverpool and Athletic.
2-Camp Nou, Wembley, Allianz Arena, San Siro, Stade de France
I would take United off that list, because OT seems like a library when ever i see them play. I'd put Galatasaray ahead of them. Liverpool are good on european nights, but from what i've seen are not one of the best in league games.
Dortmund fans are awesome...
Was going to go to that game, but i couldn't