These two lenses have been compared left and right a lot. I was in the same predicament a few months back.


I decided to go for the 17-55 2.8 ISU because I need the wide end. I've been to events and social gatherings and I sure can say that 24mm isn't going to cut it when you want group shots not unless you're outside and/or have a lot of space to move back on. Most of the time, the events I've been to are in limited space. The IS is a plus too. A good low light lens, 2.8 + IS combo.


But I voted for the 24-70 because you've mentioned that your going full frame, though still not sure when. So I'm voting based in the long run of the lens you'll be using. If you're going to keep your APS-C camera then I would suggest you go get that 17-55 now then get a copy of the 24-70 after you get your full frame camera. Also, though the 17-55 has the same glass as that of L lenses, having a lens with a designated L and a red ring is something. I hope to get one of those Ls myself


Either way, you won't go wrong. It all comes down to your preference on shooting. Would you need the wide end or an extra reach on your shots?


Go pick your poison [:P]