Weekend 1 for sure because the weather was better. We got 2 extremes and something in the middle would have been preferred, but the heat zapped the crowds energy weekend 2, you can't go all out all day everyday in that kind of heat. It made some of the day shows into pure survival. Sure it was a little chilly at night on weekend 1, but nothing a sweater and hat won't fix. Also it allowed for all sorts of costumes. It was near impossible to escape the heat weekend 2 let alone dress up a bit. Plus if you were dancing you weren't cold anyways.
Of course both weekends were amazing, but the surprises, better grass and weather go to weekend 1.