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read the review. also, look at slrgear and photozone.

the 17-55 outresolves all other standard zooms available for Canon (a consequence of being designed for APS-C sensors). it's shortcomings are in flare resistance and mediocre bokeh, and its color is slightly cooler than typical "L" optics. the build is upper-midrange, so high-quality plastics and no sealing. but it's not like all "L" lenses are sealed anyway. weather-sealing is relatively new, and even then, many of them still need a front filter to complete it.

it's a big upgrade over an 18-55, and i'd take it over a Tamron or Sigma equivalent or 17-40L any day. i don't think the 17-40 makes for a great standard zoom on an APS-C camera...it's shorter than usual, a stop slower, and isn't particularly sharp. all you get over an 18-55 is build, color, and USM.

A good summary that the OP should find very helpful. I'm perplexed by the statement about temperature, though, since my 17-55 definitely errs on the side of warmth, sometimes producing images with a distinct yellow cast that I have to correct in post. In this regard it's the exact opposite of my kit lens, which consistently renders colors much too cool in temperature.
 
If you can afford it I would highly recommend the 17-55. Otherwise the 17-40 will work for that focal range but you lose 2.8 and IS. I don't recommend 24-105 as a "walk around" because 24mm breaks in the worst spot on a 1.6.

If you do rent the two and compare them there is no way your going to want the L over the EF-S. The 17-55 smokes it in every way. I also wouldn't worry about resale. Keep the box and if you want to sell use Ebay. Canon lenses hold there value well, even EF-S ones.
 
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