Since you said arc, I'm going to cheat just a little.
But after seriously spending a lot of time thinking about this question, I honestly think my favorite material from this industry is Marvel's space material that began with Keith Giffen's Drax miniseries and Thanos series in 2003, maybe, and ended, for all intents and purposes, with Dan Abnett and Andy Lanning's Thanos Imperative a year or so ago.
I realize that includes quite a few books/arcs, like Nova and Guardians of the Galaxy and War of Kings, etc. But all of those things are connected, and all together, I think it's the best stuff I've ever read.
*Sniff, sniff* "Damn it, Diana...If I'd known they would trade us in for a JT Krul-written Captain Atom and "The Savage Hawkman," I'd have let Superboy-Prime destroy all reality.""Superman flies and is really strong...what the fuck else do you need to know?!"
-- Hitler, expressing his displeasure about DC rebooting and complaints about continuity