Annihilation by a mile. While Civil War was on a grander scale for the masses, Annihilation was more epic and its repercussions are still being felt, whereas the repercussions of Civil War have kinda tailored off for repercussions of Secret Invasion and now Dark Reign. Annihilation's repercussions are still holding strong and creating/driving stories to this day. Of all the titles to come out of Civil War, most weren't that great or have tailored off, but Nova and Guardians of the Galaxy have remained consistently great issue by issue, and the two spin off epics, Annihilation Conquest and War of Kings, were both phenominal.
The event itself was also better than any of the other issues because it just felt so amazing in scope, character's grew, no one felt like they were belittled or deminished in the event, even the deaths all felt meaningful and were well done (Quasar and Thanos specifically). Whereas Civil War, Disassembled, House of M, and others just tore down characters, continuity, and development... Annihilation rebuilt the entire Cosmic line and most everyone agrees that it's in a better place now than it was prior to the event.
In my opinion, Annihilation and what's come fromit is by far the best event over the past 10 years and potentially the best from all my years of reading comics. And this from a guy who couldn't give a flip about Cosmic Marvel prior to Annihilation.
LOVE IT!