I would say that Nashville or Washington have the best chance against the Penguins due to their superior goaltending. However, the Penguins are a strong team and it is going to take a repeat of tonight to finish them off in game seven.
I think offensively, the Oilers would be able to bring it to the Penguins. They lost their two season games, but were within a goal both times. Also, out of the 5 goals that the Oilers scored, McDavid got a point on four of them. This could be a series where McDavid could open up and be a game changer. The Western conference seem to know how to handle him better. I am not sure if the Oilers would win, but I think they would have a chance.