Penta are probably not in too bad form, as they have good fights up against Dignitas and Publicr. Se. However, the huge loss to Na'vi looks worrying, as it is on D2, which is probably SK's favourite map. I do however expect Penta to ban this map.
The thing is, Penta are quite good at contesting with T2 and T3 teams, but tend to be destroyed against T1 teams, which may be a sign of inconsistency, or perhaps they give up hope before even coming up against these teams. I do hope it isn't a fact of pure skill because that would worry me that they can't even contest with these top teams.
SK have been highly underrated in their previous games, and are in fact ranked higher than Penta in the T2 Rankings. They have caused quite a few upsets recently beating HR, Gplay, and Acer. I think that SK were underdogs because no-one had heard of them and simply assumed they were bad. Well in this case, people may over-hype them in this game, because people know they have the capability to defeat good teams.
Overall, I would just about say that this game is too close to call, and I believe either team could win. I would reccomend you bet on the underdog, whoever that may be. It's a BO3, so there's no hope of skin return like a BO2.
Go with your heart, and your mind (Underdog) and bet on whoever you choose! If I HAD to choose, I would probably put SK Slightly ahead of Penta, only because of their recent form.
Good luck, and Happy Betting!