My vote is the 24-105. When I go out I take a 7D and the 24-105 and leave the rest at home. If I'm feeling really froggy I'll throw the 50mm 1.4 and a gorilla pod in a bag. And most of the time, no cases. Just a rapid strap.
I haven't found a situation yet that is impossible with that combo. I guess if you were shooting mega landscapes it wouldn't work so hot. But then again I've got some solid shots with 24-105 and the f4 actually helped with the silky water
Thinking back before I asked for that lens, I was worried about background separation and low light and such. Neither of those has been a big deal for me though now that I own it. And the convenience of not changing lenses all the time far outweighs the times when I need to think about creative workarounds.
One thing I did buy though which I love is the pinchy lens cap. That was a nice upgrade.