The tamron is the cheapest probably because of it’s quality. I should know as I have one!

At 18mm it’s very very distorted although this can be corrected with photoshop. At 200mm results I’ve had on my Canon 350D have been soft, even at shutter speeds of 1/800th!!!

Around 38mm to 150mm is usually quite good. If I hadn’t of bought an L series canon lens (100-400), I probably wouldn’t have noticed the above as much. I’d go for one of the Nikon’s.

HTH,

Alex