Let me start off by saying that the Federer-Djokovic-Nadal "three way rivalry" has produced some of the best matches in our sport. The way these 3 match-up with one another always translates for entertaining tennis one way or the other.
#1. Federer-Djokovic
Federer-Djokovic has always been the most unpredictable rivalry, they produced great matches more consistently throughout the years. Djokovic may not have Nadal's fan base/charisma as an opponent for Federer, but I was entertained a lot more by this rivalry than any other. The fact that there's not exactly any love lost between the 2 probably spice things up as well.
#2. Djokovic-Nadal
Since Djokovic became a force to reckon with in 2011, this rivalry has always been interesting. Djokovic can go toe to toe with Nadal on any surface including his beloved "clay" which made for a more even match-up anywhere they met. The momentum has shifted from time to time as well which helped keeping things interesting.
#3. Agassi-Sampras
The 2 players of the 90's. Arguably the greatest server of all time vs one of the best returner in history. Agassi may have had a bit of a mental issue against Pete, still when you look at the H2H, it's not so bad. The fact that both guys were playing offensive tennis was fun to watch. Pete had the edge on grass and at the USO while Andre had the edge at the AO and on clay.
#4. Federer-Nadal
The reason I'm putting "Fedal" at #4 is because the rivalry got stale after 2010. Out of all the others I've listed before, I think this one produced the most "classic" slam finals of them all, but the 6 year stretch between FO 2011 and AO 2017 has been IMO highly forgettable. Sure it's always fun whenever these 2 meet because they are 2 of the greatest players of all time, but so many of these matches were one-sided or on clay that I just can't rank it above the other 3.
One thing I'd like to add about the AO final. I think it's extremely overhyped and overrated right now. The match was OK and had some drama especially the way it played our in the 5th, what was on the line for either guys was interesting etc...But the match itself was very up/down for either guy and definitely not the best match they produced. Age surely plays a factor in they're performance level, I get that. When the hype dies down and the dust settles, the story around that match may have been great, the match itself was OK but definitely not the best these guys produced.