Originally Posted by vachss
As an owner of plenty of L lenses I really disagree with this. The L designation is only used for full frame lenses, but the 17-55 EF-S has optics that are at least the equal of many L zooms. I've owned both the 17-55 and the 24-70L in the past and think that the EF-S is actually the sharper of the two. Certainly it has a more useful zoom range on crop bodies (and it has IS). I will agree that the build quality isn't of the "main battle tank" level used on the 24-70, but that's about the only area in which it suffers by comparison. Once you add the 17-55 into the mix the 17-40L becomes pretty superfluous as well.
I've often heard the argument that EF-S is worthless if you're ever planning to go FF. The problem is that if you have a crop body today then EF-S lenses may very well be your optimum choice today. Good lenses, L or EF-S, can always be sold without much loss. If you go FF, sell your EF-S lenses and buy the lenses you need then. Likely as not, though, even when you go FF you'll want to keep a crop body around for some things and may decide to keep your high quality EF-S lenses after all.
To the OP I'd ask what problem are you trying to solve? L lenses can be the right choice for some things, EF-S lenses for others and manual focus primes for still others. For high quality general purpose use I'd recommend the EF-S 17-55, for shooting in a war zone or inclement weather I'd recommend the 24-70 (and a 1-series body), for low light and shallow DOF subjects nothing beats fast primes.
Originally Posted by hieu1004
I've owned all of the lenses in question and have used them both on my 7D and 5D Mark II - so I'll give my 2 cents.
The 17-40L is a fantastic lens but is a little soft at the corners when stopped down. This lens shines on FF, so I would pick the 17-55mm EF-S lens if you're looking for one around this focal length. It's faster and has more range - more ideal for a crop camera.
24-70 and 24-105 perform very similar, but I prefer the 24-70 because of the 2.8. It really comes down to range vs aperture, what do you need? IMO, a 24mm on a crop sensor is not that wide (if it's going to be your widest lens), so it all depends on what lenses you have currently.
The reason why I have the lenses with f/4 aperture on the list is because I'm fine with that aperture for filming. I currently only have a nifty-fifty(50mm f/1.8) since that will always be my backup prime. I wanted to start fresh and this is where I've ended up. My plan was to get a 70-300 f/4-5.6 IS USM for track days and whatever else lens for everything else.
What I'm trying to determine is a lens as my go-to lens for video AND photography. After a long night of reading and comparing, I've narrowed it down to either the 24-105 f/4L or 17-55 f/2.8. Both seem to be just a tad sharper than the 24-70 f/2.8(not to mention the price tag). Since I'll still be using a crop sensor, it seems like the 17-55 f/2.8 could be the winner. How would the 24-105 f/4 be more superior? Obviously the L series' standards(weather proof) is a big one.