I voted Michelin but that's only based on my friend's experience with them and he uses his bike for commuting and leisure. I use my bike for training/leisure and have been very happy with Michelin Krylion Carbon which are currently very difficult to get hold of so I'm using Continental Ultra Gatorskin.

The ride is a lot harsher than Krylion but I'm hoping I'll get very few flats (I was already impressed with Krylion's flat resistance - is there a petition or something to get Michelin making these again?) in return.