I don't think I played any other teams than Spurs and Napoli on PES2012, but I played a few matches today with Barcelona on 2013... I mostly played against Real Madrid though, but I completely tore those fuckers a new asshole.
I usually manage just fine with Spurs, but I have to admit that using Barcelona was easy mode. Messi hat-trick in two matches, and one by Pedro with red arrow
All in all, online is really a pathetic excuse for fun tbh, I won't be playing online much more this year either as I prefer even matches with friends over this bullshit.
A very nicely working tactic set online;
4-3-3 (Close to Barcelona default, but narrower SS's, the central striker can either be Messi type SS or Torres type CF, I hardly notice any difference tactically) or 4-2-3-1 (Riskier, but even more powerful offensively, I only use with teams that got two decent Box-to-Box midfielders as CMF)
Possession
Support 10
Distance 10
Style 10
Pressing 13
Def Line 14
Compactness 8
Push defenders up around the same level as default Arsenal or Barcelona, sidebacks more or less on level with the CD's but hugging the side line and CD's a bit wide (either side of the half circle on the edge of the box is a nice measurement). The DMC will drop down as an extra defender and mark their striker, and pressure 13 along with compactness 8 will make sure you keep decent lines. I had more than 60% possession in all matches today, something I usually manage with Spurs as well online (going to be harder without Modric though), and I played risky and offensive and not trying to hog the ball. I was going for massive attack goals galore.
This setup will work your midfielders like dogs, but it will give you loads of passing options offensively and you can really lay siege on opposition box, forcing mistakes and re-win the ball until you eventually force it into the net. If you are trailing, move sidebacks up to midfield line, add "swap wings" and go one step more offensively on the attack level bar.