I'm not much of a fan of Co-ops.  They're more of a puzzle than a game.  And there is the groupthink problem.  I don't feel like I'm playing a game when everyone else is discussing what I should do on my turn.
That said, some of my favs are partial co-ops.  BSG, Dead of Winter, Last Night on Earth, etc.  Those are more either team games, or co-op with individual goals.  But most of my favorites are competitive games.  I get enough co-op gaming while roleplaying.