If I was going to pick a single ense to use, I'd go with the 24-70 f2.8. It will depend somewhat on whether you are using a full-frame or crop sensor though. And you're probably better off having a couple of lenses with you, so you could have some extra zoom length available if necessary.
Also, if looking for advice on wedding shooting gear, whether lenses or whatever, I'd highly recommend the courses over at www.creativelive.com
They recently had a course with Zack & Jody Gray
that was fantastic, and is quite affordable to download: http://www.creativelive.com/courses/wedding-workshop-zach-and-jody-gray
They also have some courses scheduled for the future on wedding photography, and all their courses are completely free to watch while they happen live.