Without a doubt, golf.
Honestly, I think the only fair way to really compare golf and tennis is to put Maria Sharapova up against Natalie Gulbis. By far they are the hottest women in tennis and golf.
Although both Maria Sharapova and Natalie Gulbis are hot. I'd have to go with Natalie Gulbis. Any chick that looks like her and can golf, as far as I'm concerned, is perfect.