The 15-85mm would be a better choice, or if you want/need a faster aperture, the EF-S 17-55mm f/2.8 IS. Both deliver L-series optical quality, both perform slightly better than the 24-105mm on a crop body.

In fact, 24mm on APS-C is not even wide angle - it's 38mm FF-equivalent, meaning in the normal range. The 24-105 has better build, including weather sealing (but you'd need a sealed body, e.g. 7D, to benefit from that).

For a crop body, I think the 17-55mm is the best general purpose lens - indoors and out, landscapes and even portraits (f/2.8). The 15-85mm is a great outdoor walkaround lens, but will likely need a flash indoors.