The 17-85 is the oldest and worst and cheapest of the three, and has been replaced by the 15-85. Nobody knows what the 15-85 is like, yet, as it isn't readily available, but on paper it looks like it's going to be an improvement over the 17-85.
The 17-55 is the fastest and most expensive of the three, and is widely regarded as the EF-S equivalent of an L lens, at least as far as sharpness is concerned. It's also f/2.8, which makes it available light capable.
All three lenses are EF-S and cannot be used on full-frame cameras like the 5DMkII. All three lenses are IS USM, which means stabilized with a silent autofocus motor.
However.
There are a ton of walkaround lenses in the Canon lineup. If you're willing to pony up the dough for a 17-55 IS, there are also a few L walkaround zooms to consider, particularly if you tend to shoot at the long end of the zoom more than the wide end, and you're considering upgrading to a full frame in the relatively near future. These would include:
EF 16-35 f/2.8L II USM
EF 17-40 f/4L USM
EF 24-70 f/2.8L USM
EF 24-105 f/4L IS USM
Ls are bigger, heavier, and more expensive, but the exotic glass in them tends not only to give good sharpness, but also better contrast and CA control. It is, however, a subtle improvement and is often not worth the price jump for most folks.
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