[Liam O'Neill]

I have the Tamron 28-75 and I love it. With either of these two there is an issue about quality assurance from the factory, and you might have to try a few examples to find a good one. Make sure the shop will be happy to work with you in getting replacements if your not happy. I was lucky, the fist one I bought seems perfectly fine to me. I get the impression the Tamron's aren't quite as prone to this as they used be.

I don't really know why I went for the Tamron over the Sigma. I just got an impression for reading all the reviews I could that the Tamrons were generally better, but that wasn't based on anything scientific. Because I was replaceing a 28-80 lens with it, the funny range on a crop camera didn't bother me at all (and I'd bought a 17-35 to complement it anyway)
I think today I'd be very tempted to look at the Tamron 17-50 2.8.(they didn't make this lens when I bought mine) It should be just as good (I haven't read enough reviews to really know if it is or not) and has a more useable range on the crop (it's basically to a crop camera what the 28-75 is to a full frame)

I love mine, it's as sharp as anything, (it seems sharper than my 70-200 F4 L) and just feels right on the camera, and to my eye the pictures from the camera need very little tweaking. OK, the AF is a little noisy and not lightening quick, but it's not like it doesn't work. The filter size is unusual, though it's the same as the equally quirky 70-200 so I don't mind. I LOVE Tamrons lens cap. That may sound silly, but once you've used the Tamron cap a few times, you'll want one for all your lenses. It's the lens that lives on my camera and the one I use most often, and it's never let me down.

If you get a good copy of the Tamron, and there are good ones about, you will love it, though I suggest you seriously look at the 17-50 2.8 too.