Yeah, Barca are playing well but it really does depend on who the opposition is, who the manager is for tactical reasons and whether the opposition has a fully fit squad (or if Barca are missing key players). It isn't a foregone conclusion but at the moment my bet is from most likely to least likely:

Barca
Liverpool
United (yes, I still think they can turn it around!)
Porto
Chelsea
Arsenal
Villareal
Bayern