4-2-2-2 is probably my favourite, and it can be used with any team ever. 1 DMF, 1 CMF, and 2 OMF's in midfield. I play mostly against humans, and I am rarely beaten (on PES4) with this set up.
I know I've slagged my formation thread all around town, but you may find it usefull. Click the Advanced formations link in my sig for some special set up ideas. You'll find more detailed info on the 4-2-2-2 I suggested for a Barca set up too. Hope it helps.