I haven't seen Watchmen yet (blasphemy!), so I can't make a judgement, but it looks pretty damn epic

V for Vendetta was good, I haven't yet seen Batman Begins or The Dark Knight, and I bought The League of Extraordinary Gentlemen today, special 'Definitive Edition'. I haven't seen From Hell, though I may at some point, and I've seen too many Marvel films to list. Overall, I'd reserve judgement personally until I've seen a few more of the ones on my list above that I've not yet seen, but at present my vote would have to go to TLOEG.
Alan Moore distances himself from the filmed adaptations of his works, with good reason, since they don't truly follow his comics, and he's severed all ties with DC after the way they've treated him and his collab. partners and friends over his comics and in some cases their films too, but at the same time, it's the filmed adaptations that have gotten me interested in his works, so that's got to be a plus for him. If it wasn't for V for Vendetta, Watchmen and TLOEG, I'd never have gotten interested in his works and wouldn't now be planning to
steal buy some of his comics.