When are you getting a FF camera? If your answer is anything other than "very soon," I'd really recommend considering the EF-S 17-55mm f/2.8 IS. Optically, it's as good or better than the 24-70mm and 24-105mm (on a crop body), it combines two excellent but mutually exclusive features of the two L lenses - f/2.8 and IS, and the 17-55mm gives you a wide angle portion of the zoom range (24mm on 1.6x is normal, not wide, which is <35mm FF-equivalent). IMO, the 17-55mm is the best general purpose zoom for a crop body, and would pair wonderfully with the excellent 70-200mm f/2.8L IS II, giving you f/2.8 IS coverage from 17-200mm (and you won't miss the 15mm gap).