Well i have the 24-70 EX and its a beast. only got it yesterday and have taken about 200 shots indoors and i like the IQ but im going to take it back because its just too big and heavy for a day out.
Im thinking of getting the 17-70 but i must admit i would like a longer reach and faster apature at the long end. i just cant find anything that has the same spec only smaller and in the same price range.
Well I'll let you know how they compare! In the end, the higher IQ of the 24-70 and constant f2.8 was driving me nutso and I shipped the 17-70 back. Plus, I got a DSLR to take better pictures, not to have a more expensive point and shoot. I figure a 10-20 or 10-22 will round out the collection to completion and make me feel like I'm using my camera for it's intended purpose. Seriously though the 17-70 is an awesome performer I think, and 4.5 at 70mm really isn't that bad at all. You're only other option I think in the same focal length would be the 17-85 IS, you don't get the faster aperture but you do get IS, which may or may not help with indoor shooting. I did take some sample pics with the 17-70 at 1600 ISO and it did well also, I just failed to post them before I deleted them.