I parted with an older EF 28-70mm f/2.8 L USM and picked up an EF 24-105mm f/4 L IS USM soon after. For my needs, it works really well.

Why?

1) I have several wide aperture primes if I need to shoot in low light – Sigma 35/50mm Art, Canon 85mm f/1.2 L II – so the f/4 maximum aperture isn't terribly limiting
2) The focal length range makes the 24-105mm lens an excellent choice when photographing posed shots at a wedding (bridal party formals, etc)
3) Its focal length range also makes it a good studio lens, especially when you're set up in relatively space-limited areas. You can set up a tripod and choose dramatically different framing between 24mm and 105mm without having to move the camera.