I think that the Marvel Universe fits much better together (ala the Avengers and Co.) than the DC Universe does (Justice League), moreso because the Avenger's stories seem relevant. Everytime I read something about The Justice League it's about some extradimensional threat bent on destroying the universe (coming from *shock* another alternate Earth) and... uh... zzz... gurgle... hm? I just don't see it being relevant to me, so I can never get into it (However, Tower of Babel was great... because it takes place on one Earth, and Batman theoretically kicks butt).
For the avengers, we have stuff like Civil War, Secret Invasion, and Seige which I find to be fantastic stories that incompass all of the Avengers.
Still, if it's one comic universe I love beyond all others, It's gotta be Batman's universe. Gotham City is wonderful to be a part of (although I would never want to live there, and I continue to wonder why anyone does. 
) Batman is great, and the villains are ever greater. Besides Jim Gordon, I'm not too fond of Batman's supporting cast (Batman always works the best when he's alone 
).
My favorite Batman Graphic novels are...
1. The Long Halloween
2. Year One
3. The Killing Joke
4. Dark Victory
5. Arkham Asylum
My favorite Batman Villains are...
1. Scarecrow
1. Two-Face (I really can't put one in front of the other, they're both so great!)
3. The Joker
4. The Riddler
5. Hush
