Porto are a step up from the competition here, and that's the truth. Their sucesses under Mourinho gave thm financial leeway to get a decent squad and they're regulars in the last 16 of the champions. Last season Porto finished a clear 20 points ahead of 2nd place Sporting. This season they started off badly, mostly because of the whole Quaresma issue. They're a solid team, and Lucho is the man to watch. A very good playmaker, likes to set up his partner Lisandro López, a very efficent striker. Also, Hulk is a powerhouse. Watch him especially on counter attacks, if you give him space, he'll go all the way. Strong, fast, with decent skills and a powerful kick. Their defense is pretty solid, with their major weakness (left back) beeing fixed in the winter transfer period. The goalkeeper is indeed the weakest link. Helton is a very good goalkeeper, but he's having an atypical season, conceading some unnusual goals.
Also, don't let the bayern results fool you. Yeah, we took 12 from them, most of them stupid goals. And we beat porto for the League cup 4-1 in the semis, lost to them in the league at home, and drew away. Every game is different, and if there's one thing our manager has on Jesualdo Ferreira (porto's manager) is that he knows how Jesualdo thinks, and knows how best to counter him. In the years they've managed both clubs, Sporting have lost once or twice to porto, having faced them on average 4 times each season.
So to me, their weakness is the manager. You read him well, you take 'em out.
They play in a 4-3-1-2 with 2 defensive midfielders, so that gives them extra coverage in front of their defense.
And don't underestimate the players, or the away game. Jesualdo is nowhere near a José Mourinho, but his team is way better than Mourinho's team was.