I'm not inclined to disagree with Tim as he is far more knowledgable than I, and it is a matter of personal opinion, of course, but I prefer the 24-70 on my 50D (which is the second camera to a 5D2).
It's rare that I can't get wide enough even on a 1.6 body. If I do hit that wall, there's always the fairly inexpensive Sigma 10-20 that I keep in my bag for very wide shots anyway. I thnk the 24-70 has a little more to offer from an IQ perspective. IS would be nice, and there's been talk about an IS version of the 24-70 coming, but I don't feel like I miss it at this focal range. It's very rare that I can't get a fast enough shutter speed to safely hand hold. My copy focuses very well, though it may or may not be as fast or consistent as a 17-55.
The 17-55 is very popular for good reason. If you were to do a poll, I think it would gather more votes, but I'm real happy with my 24-70.