I prefer D&D to RIFTS. Of course, it's hard to compare the two, given that one is a fantasy RPG and the other is a genre mish-mash RPG. I will agree with the analysis of others that one of D&D's advantages is that an average GM can run a very fun game with little effort. RIFTS, on the other hand, requires more effort and skill on the part of the GM (and the players) to make the game fun.
I played in a very fun RIFTS campaign set in Russia. We had a lot of fun roleplaying, and a diverse group worked well together. The DM put some limitations on what we could play, but there were plenty of options available. We had a psionic, a ley line walker, a Mystic Kuznya (basically a magesmith), and a bounty hunter. Everyone was combat capable, even if some were better in certain areas, but with different skillsets everyone had different opportunities to shine outside of combat.
I am not a fan of the RIFTS system. Although not unplayable, there are a lot of issues that cause problems, and a GM and players will need to make a lot of judgment calls and/or house rules to make the system playable. The setting is interesting and has a lot of good ideas. It has some issues, but it is a game world, after all, and there aren't that many game worlds (or fictional worlds in general, for that matter) that don't have some holes in them. The system can be made workable, as long as everyone is on the same page about things and willing to roll with it.