@Walter Hinteler,
I don't know why people get so excited about Federer-Nadal. Yes, they had some amazing matches ten years ago. If you want the best rivalry on grass today, you clearly want Federer-Djokovic, maybe two of the best grass players of all time. If you want the best rivalry on clay, you want Nadal-Djokovic, probably the two best clay players of all time. I think it is amazing how Djokovic flies under the radar when Federer and Nadal are around.