Okay, so I think that Mega Man 2 and 3 might be better, but I still think 6 was a good addition to the series, and I'm glad Nintendo brought it to our shores. Destructoid gives nine tongue-in-cheek reasons why they feel that 6 deserves top honors, from the music to the entrances of the Robot Masters, and more.
Of course, I warn you with utmost urgency that Destructoid is a bit more coarse in its language and humor than we are here at The Mega Man Network, so proceed with caution if you choose to view it. Some might not find some of the subject matter to be especially safe for work, school, or family looking over one's shoulder.
If none of that bothers you, it's a pretty solid article to enjoy.