That's neither here nor there though, the fact is Federer-Nadal rivalry for me has become unexciting as a Federer fan to watch because of the way Federer has folded mentally against Nadal. I agree that it is a bit unfair that Federer did not have a lot of chances to "even the score" so to speak when he was at his prime because Nadal wasn't showing up on USO finals until recently but it is what it is. For the reason alone that both Federer and Djokovic have the self belief that they can beat the other player on their best day at any surface makes this rivalry more exciting IMO. It's not just Federer though, watching Nadal vs. anybody on clay is pretty much NID and makes for a pretty boring rivalry.
While I agree to a degree I would content that Nadal-Djokovic rivalry is the most enthralling in tennis today. Their grinding battle of attrition is actually pretty exciting. Considering Federer is now beyond his prime I really don't get excited by any of his so called next gen rivals. Despite the successful aberration of an year he has been having, he won't be able to sustain it next year -- I feel it is his last hurrah. It's almost a given that he will end of with a negative H-H against Nadal, Djokovic, Murray et al. if he persists in playing for next few years further into his decline.