Venus and Serena Williams
These are hard - I've never thought about which doubles team I root for the most, to never lose. And given doubles players swap partners so often it's hard to keep cheering for teams and not individuals players.
But, when Venus and Serena play slams, I definitely want them to win. I really like the Bryan Brothers, but I'm not bummed when they lose. When the Williams sisters compete in Grand Slam tourneys, they expect to win the slam and I expect it as well.
I've been lucky enough to watch Team Williams win a few matches at the Beijing Olympics and when they step on the court together they are fierce and so much fun to watch. The sisterly love and giggles between points followed by cracking serves and forehands is fab. It's during doubles that you can see how much these two love the game, and each other.
Two Olympic gold medals, 12 Grand Slams.
Runner up: Rafael Nadal and Marc Lopez aka Team Cute