As a fan, I don't like the seeding, with my favorite 2 teams in the world going up against each other. But I guess I'll have to pull more for Barca over Arsenal, but I'll cheer for both if they do well. Barca though is a pretty powerful squad, more powerful than Arsenal.
As for Bayern/ManU, outside of Germany, you'll be hard pressed to find ANYONE who chooses Bayern over United. I would LOVE if Bayern would win, but it probably won't happen.
As for Inter/CSKA, if Barca goes through it doesn't matter who wins that draw, but if Arsenal surprisingly makes it, it's CSKA all the way. Actually, CSKA is who I want to win regardless because it will be an easier challenge for Barca or Arsenal.