Zoom for APS-C Camera, Canon 70-300mm, Tamron 70-300mm or????

Uh, you might want to recheck Photozone. They rated the 18-200 at 1.5, and the 15-85 at 3.5. The 18-200 suffers, as do all superzooms, from a collection of compromises necessary to get the overall range; that doesn't make it a bad lens, it just makes it a lens that emphasizes convenience over image quality. The bottom line is that, barring QC issues, your 18-200 should be thoroughly outclassed by the 15-85.
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WLW