This is such a funny debate to me.
If we're talking about a Spidey film trumping The Dark Knight in terms of money, then yes. All it'll take is a critically acclaimed Spidey film (much like part 2) that just grabs people at the right time, and doesn't let go. Simple as that.
If we're talking in terms of it being a better movie, then we're going into the realm of OPINION. That's right, opinion. In my OPINION, Spider-Man 2 was a better film than TDK. It just had more emotional weight, as well as some more indepth characterizations...not that TDK didn't have those things, but I just felt that SM2 resonated a little more with me. The only things I would change about SM2 would be the unmasking scene, and Kirsten Dunst's teeth.
Also, much like Batman Begins, I just don't think Christopher Nolan has quite gotten the hang of action sequences. I think there could have been a bit more done, especially in the final confrontation with the Joker, which was filmed so that you couldn't tell who was hitting who at one point. Still, the chase sequence and the sequence of Batman fighting the police and the clowns made up for it. The only thing I would change about the Dark Knight would probably be to NOT kill Harvey/Two Face at the end. His character may have served the purpose for this film, but I think there were more stories to tell with the character. Also, a little more
Batman/Joker action.
NOW, these things being said, I am a Spider-Man AND a Batman fan...a little more of a Spidey fan, though. SO, it stands to reason that I'm going to favor the best Spider-Man movie over the best Batman Movie. However, the general public is a fickle beast. Batman is their favorite todya, but if a hot, new superhero flick comes out next summer, and it is well-recieved and does well financially, you can bet that just as many people will be on here and elsewhere saying it is "The BEST superhero movie EVER". THe following year, the same thing.
Honestly, I think, in about 5 years, we'll see how Dark Knight holds up. I love it, it's a freakin' PHENOMENOL film...but it's still new to me. Spider-man had that effect. I watched it alot, then I didn't watch it for awhile. When SM2 came out, I couldn't walk by a television showing it and not stop to watch it...
....I still can't. THAT makes a damn fine movie, and I hope that TDK has me doing that 5 years from now.
(also, Heaven forbid someone likes both Spidey and Bats....Jeez)