Well having followed the testing over the last couple of weeks, I feel that Ferrari and Red Bull are the current pace setters, maybe Ferrari are even slightly ahead. I dont know where McLaren are at yet. I dont think they're quite up there with Red Bull and Ferrari but they arent far behind. I watched Vettel complete his race simulation the other day with stint times starting in the 29s and falling away into the 31s by the end of the stint. Button did the same (although we dont know the fuel loads and tyres), so i dont think it's all doom and gloom at McLaren yet, they just need more time.
I think whichever teams can get a handle on the tyres will prevail. It'll be all about durability because it's better to be 0.5-0.8s a lap slower over 20 laps than be forced to make an extra pitstop.