EF 24-105mm f/4L IS, all the way. IQ is excellent and the extra reach will come in handy. For all these zoom lenses you have to consider IQ after processing and correction, not out of the camera. All the leading programs correct for both of these zooms' known weakness at their wide ends.
Here's my trips to NYC last year, all taken with the 24-105mm:
http://www.flickr.com/photos/dcstep/...7623758624662/
Here a Fave, out the cab windshield in a light rain:
Flatiron building from our cab by
dcstep, on Flickr
Dave