Batman.
I love most of DC's heroes (I'm not a big Marvel fan) but Batman always comes out on top. I love Green Lantern and The Flash, mostly thanks to Geoff Johns, but Batman has the best stories with the likes of The Long Halloween, The Dark Knight Returns, Morrison's run on Batman & Robin, Year One, Arkham Asylum: A Serious House On Serious Earth etc.
Batman is relatable and inspirational (insofar as he's human and yet a superhero), he has an amazing support cast and the best rogues gallery in comic book history.
I'm actually so tired right now I can't give a decent argument for why I love Batman as much as I do but, believe me, I love him more than you love your mum.
The Green Lantern universe lends itself to being a gigantic, Star Wars-esque space opera, as shown in the Sinestro Corps War; the Flash has a fantastic dynamic with The Rogues and the creative ways which writers utilise his powers always makes me smile; Superman is fucking Superman but Batman is... he's Batman! Sigh, I love Batman.