Williams X2, period. I don't consistently root for anyone else. If one of the my girls loses early I root for the other and if they both go out I usually force myself to watch the rest of the tournament. They're the single reason I started watching tennis (well, women's tennis) and the reason I continue to watch. If I didn't consider Sharapova their main rival I might be a fan of hers...but her shrieking does get on my nerves a bit. I know the sisters grunt too but it's not as high pitched and torturous to me.
As for the boys, SAFIN (obviously) FERRERO (who i've met) and Federer b/c he's just amazing.
Serena: Queen of the odd in OZ.
Venus: Please follow suit and win Wimbledon again.