I said "yes" because right now, there's no doubt in my mind that it is my favorite. On the other hand, my tastes in things change easily, and change a lot. My love of D&D has endured these many years while seeing the rise and fall of many other interests, but I think that's mostly due to the fact that I haven't really played or read that many other RPGs.
Since I got to college, I've read Call of Cthulhu d20, which I love and am dying to run, but surprisingly few of my gamer/nerd friends are in the know about the writings of Lovecraft, so that nixes that for the immediate future. Even if I could run/play it though, I'd have to go back to D&D for my fantasy fix, as CoC's hopelessly nihilistic cosmology doesn't appeal to me every day of the week (when it does, man oh man it does though).
I also got a chance to play the Serenity RPG. The campaign I was in was an absolute blast, and it will probably always be one of my favorite roleplaying experiences ever, but in the end, being sci-fi with a fairly limited setting, I don't think it had the potential for limitless adventure that D&D does.
I even got the chance to play other fantasy games, like Fireborn and Shadowrun, but turned those down, simply because they weren't D&D enough.
So for the time being, I think D&D (any edition, I should say, with the possible exception of 2nd) will remain unchallenged on its throne as the best RPG in my mind. I recently picked up Exalted 2E though, so who can say what tommorow may bring?