By now you'd think I'd remember who it is who regularly makes the point...neuro, maybe?...but, anyway, the 24-105 on full frame is better in every single specification than any f/2.8 standard zoom on APS-C. It's wider and longer, for starters, and you can get a shallower depth of field with it, and you even get less noise with the same exposure (meaning a higher ISO to compensate for the "loss" of a stop) to boot.
If you like your f/2.8 standard zoom on APS-C, you'll love the 24-105 on 135 format.
I'm not big on standard zooms, myself...but I keep thinking from time to time that maybe one of the alternatives might be worth considering, and very quickly come right back to concluding that the 24-105 is the best for me. The Tamron has IS, sure, and an extra stop, but it doesn't have 70-105. And the Canon 24-70 II doesn't have IS or the extra range, even if its image quality is better...and it's stupidly expensive. The 24-105 isn't at all a slouch in the IQ department; quite the contrary -- it's better than the original 24-70, just not as fast.
In short, it's the most versatile standard zoom there is, with great image quality. Each of the others beats it in one metric, sure, but it beats them in two or three other metrics.
Which is why it'll remain my standard zoom for the foreseeable future. Like, say...until Canon releases the TS-E 12-1200 f/1.0L DO AF for $999.