Rafa has the most to prove. Basically, he has to prove he can beat a top hard court player he struggles with whose been playing well, when he has questions of being in the final solely due to a weak draw, injuries and poor performance and fatigue of others. Beating Nole like he did in the Olympics would really quiet a lot of doubters, and prove that he is one of the best not just on hard court, but to ever play the game of tennis professionally.
rafa has beaten roddick, nole, murray, and roger on hc, grass and clay.. on hc, he's beaten nole at the olympics and roger in one of the greatest aussie open finals of all time.. i don't think the guy has anything to prove on hc or any other surface against anyone, especially with 8 majors, including wins on all 3 slam surfaces, clay, grass and hc (the first man of his generation to achieve such a feat), and olympic gold already under his belt.. rafa also won the '08 wimbledon final, a match instantly touted the reatest final ever.. all of which means rafa's already proven he's one of the best to ever play the game of tennis, not just on clay, but on any surface..
that's why i still think nole has the most to prove today in attempting to dispel the notion that's he's nothing more than a one-slam wonder whose only slam title came at the expense of jo-willy tsonga..
all rafa has to prove is that he can win the uso.. that's all.. however, after reaching 3-consecutive uso semis, it was only a matter of time before he won this thing anyway, and no one ever doubted he would eventually..
not to mention the fact that nole trails rafa by 7:14 lifetime and needs to prove he can reverse that staggering h2h deficit..