The nearest station is North Greenwich—no contest. It’s fast, it’s easy, and it’s literally part of the arena complex. You can’t get closer unless you camp out in the lobby.
But don’t let that stop you from mixing it up. Take the river bus for the views, or catch a bus if you’re feeling spontaneous. The journey is half the fun, right?
Next time someone asks you, “How do I get to the O2?” you can say, “Easy. Just follow the metro lines to North Greenwich. Oh, and maybe bring a jacket—the dome is huge, and the air con is cheeky.”