the 24-105 is a good option, but you should have bought it in the kit, no worries as there are tons for sale used at or near the same price you'd pay in the kit. that's your choice if you want good reach and don't care if f4 is a little on the slow side. The canon 24-70 f4 is maybe a hair or two sharper, but not enough to justify the price difference IMHO. If on the other hand you need f2.8 and if you can afford it the canon 24-70ii is really peerless, however that comes at a insane (IMHO) cost. Having an extra $1000 in my pocket and IS is important to me, so the Tamron is the clear choice, at least for me, between those two lenses. Don't concern yourself with the internet babble about lens elements coming unglued, those things get blown way out of proportion by the gear patrol on the internet. Yes Roger at Lens rentals had a problem with 2 of his first 10 lenses, he has not had a problem with any of them since and Tamron quickly repaired the issue. Roger is also fond of saying Tamron has one of the best service departments in the photo business these days with three day turn arounds and rarely ever a hassle. He hasn't seen a problem since, nor have I seen anyone else complaining of that issue with that lens. My copy has worked flawlessly since day one (about 6 months now) and is noticeably sharper than the canon 24-70i it replaced and the IS really good. I can get a solid 2-3 stops when needed, I don't blink an eye now at 70mm and 1/15.