cheer federer on if you like his tennis and like him as a player.
cheer nadal on if you like his tennis and like him as a player.
cheer murray on if you like his tennis and like him as a player.
it's easy... i love federer's aggressive tennis and enjoy Nadal's a lot. I'm glad Rafa is back. i don't mind murray at all. yeah, he's a grinder, but he's such a high level form of it that it can be interesting when he plays an attacking player.
it's tennis, not football/baseball. unless one of the players is your countryman or came from the same town, i don't see how you can have such an attachment that you'd support someone you didn't even like just because he gives your avatar's* nemesis a bit of trouble.
* av·a·tar /ˈavəˌtär/ Noun. A manifestation of a deity in bodily form on earth.
If only it were so simple. Sadly there are too many glory hunters who are more interested in numbers and maintaining records over rooting for someone because you enjoy watching them play.