IMO, the 24-105mm f/4L is pretty much the ideal walkaround lens on FF. I wouldn't be too worried about the f/4 - keep in mind that the crop factor applies to DoF as well, so an f/2.8 lens on a crop body will have the same depth of field as f/4.5 on a full frame body.


Having said that, I absolutely love my EF-S 17-55mm f/2.8 on my 7D - for a crop body, I think it's the best choice as a walkadound lens, and is the one that's on my camera most of the time.