In terms of actually being a contest that either player can win, Nadal vs Djokovic is better. However despite some amazing points, it all gets a bit over the top and boring when every rally is 25 shot and over type affair. Fed vs Nadal is more entertaining but predictable in the outcome. case in point Rome 2006. The match was absolutely sick, but of course Fed blew a couple of forehands and lost the match. Nadal remained strong.
The best combination of unpredictability and entertainment is federer vs Djokovic. Close matches full of great attacking play, hard to call before hand. sadly too many of these have been semi finals, especially in slams where they have met 11 times but only in one final. crappy draws.
How to clarky - work out most or only realistic outcome, claim the opposite
Federer, Djokovic, Delpo fan (also like Nalbandian, Dimitrov, Tsonga)