Ofcourse you'll be cheering for the best team.
In sports, it's all about winning.
So, why would you want to be cheering for someone who's not winning?
The other thing is if the team is from your town, state, etc.
And since I'm not from the USA, and I'm a big of NBA, I'll always cheer for a team that's doing solid.
It wouldn't make sense for me to be a fan of, for example, Kings.
See, sometimes I want the best team to lose... I have a underdog complex, and yes the Kings would be hard to cheer for.