what I always do - I ask oppinions on the forums and then i take my camera to the local camera store, put their lens on my camera an shoot many many frames with all the lenses I am interested in. I use different focal length, and aperture. I shoot same subjects with different lens. I go home, compare the results and make a decision.
For me - it was a matter of seconds to find out that the sigma or tamron 18-200mm is not the lens for me. the focus is slow and it hunts, I took the lens off and started testing another one right away. What I saw at home just proved my findings - the quality of the shots was horrid.
By the way - I use Sigma 24-70mm EX 2.8 as my main lens. I am mostly happy with the results. For outstanding quality that no zoom can give me I use the cheap cheap cheap Canon 50mm II 1.8. It's an amazing piece of glass for the price of $120 it is the best price/quality one can get. I bought it used on ebay for $70 which made it a half the price if I bought it new +taxes ...
The Sigma 17-70 and Canon 18-85 IS are pretty good and comparable quality lens. some Sigma glass is much better then some canon glass and vice versa.
to me buying a DSLR and putting bad glass on it makes no sense. You'd get much better results with any P&S superzoom camera for MUCH less. I learned it from my personal expereince
F10 535xi M-Sport, Dark Graphite
E39 540i Sport Titanium Silver - SOLD
E34 520 Black - SOLD
Last edited by O.S.; 01-07-2007 at 10:52 AM.