Overall, the results from this test were not totally surprising. The f2.8 lenses did well (as one would expect). The 24-105 L (G) performed solid across the board --- no surprise there either. The new 18-55 IS (E) is definitely improved over its non-IS predecessor, but it's not quite at the level of the f2.8 lenses (surprise). Stopped down E does very nice, and overall, leaves me with a very favorable impression considering its weight/size, price, and having IS. I don't know what Canon did with this new "4-stop" IS unit, but it's dead silent (inaudible) and very effective. You can read DPR's information on this lens http://www.dpreview.com/news/0708/07082007canonefs18-55and55-250.asp . The 18-200 OS (F) continues to impress, test after test. E cannot match F at any FL (at or near wide open) -- at least not with the particular copy of E used in this test (I'm certainly open to the possibility that my copy of E was not the best of the lot; I just don't know).
But going back to the f2.8 lenses (B C D), very few reviews are out on the Tokina 16-50 (B) while lenses C and D flourish (at least within the online forum communities). But after using B do I recommend it over its competition? Should someone looking for a lens in this class get B over C or D (or even the Sigma 18-50 f2.8 Macro)? My answer is generally "NO". In terms of best bang for buck, I recommend C, the Tamron 17-50. Even though it has the loudest AF of all the tested lenses, and its AF in low light is not as accurate as B and D, it is the smallest in size and the lightest in weight of all the APS-C f2.8 standard zooms. Moreover, it's also the least costly in price, its build quality is "good enough" and can certainly take some abuse, and optically it's right there with the pack (depending on the given FL). It also gives a wider FOV than the 17-55 IS (D) at 17mm, though not quite as wide as B at infinity focus (though at or near MFD they are actually very similar in FOV). Of course on the tele-side of things D goes narrower to 55mm (longer than both B and C). But C is my best value lens recommendation.
D remains the "cream of the crop", hands down. This is no surprise as its price reflects its worth. It is the only one with IS and ring USM and FTM. These features alone make it unique and incomparable. Its AF is superbly swift and silent and accurate (and in low light it really separates itself from both B and C). And its optics are at least the best of the bunch too (aside from horrid flare performance). At 17mm, the f2.8 lenses are comparable in sharpness (with the nod arguably in favor of D), but moving to 35mm and 50mm/55mm the 17-55 IS is sharper and more contrasty at the pixel level. Build quality is not quite as good as B, but it's no slouch either. In short, if money is no object, this is your APS-C f2.8 standard zoom lens.
So that leaves us with B. As already mentioned, the build (objective) and build-feel (subjective) is unmatched among its f2.8 peers. Solid, robust, perfect dampening, among other perks make it wonderfully pleasant to handle and hold. AF is slightly quicker and certainly quieter than C. Optics are at a very high level also, especially at the wider end to mid-range. [Do note that CA is its weakest point.] I said above that generally-speaking, I will recommend the other lenses over B. But if you value most having a true 16mm FL with the best build quality of the f2.8 APS-C standard zooms, then this is your lens. It is priced in between C and D, so it is priced accordingly IMO.
Canon, Sigma, Tamron, and Tokina have come out with some stellar APS-C f2.8 standard zooms, which only benefits consumers. I recommend all of them heartily, and this recommendation is not so much based on optics (because they are all excellent at day's end) but on specific needs and budgets.
[The image above is taken with the 18-55 IS]