Real Madrid. Good starting team, Ronaldo, and Benzema and Higuain mature very well indeed. (I focus a lot on attacking play). In my current season, I've also had a takeover so the large budgets add to the enjoyment.
Aside from that, the team I support - Arsenal. Always a nice challenge to lead them - and in the game, stupid Barca players don't try to unsettle Fabregas!
Man City is enjoyable for the large transfer budget but as said above, if I beat Arsenal I simply can't play anymore. I love Arsenal too much for that.
Cardiff is a good one if you're looking to get a Championship side into the EPL.