Sigma or Tamron

I have a Pentax k100D Super with a standard 18-55mm lens. I want to buy a 28-300mm zoom so I wont have to keep changing lens all the time. Sigma and Tamron both do one in this range that retail for about £200. My dilema is which make to go for. I have looked at the specifications for both makes and they look very much the same to me, although I am no expert on this subject. Anyone out there got any advice or suggestions. Paul.

I have used both Paul. Not the 28 to 300mm but the 70 to 300mm versions. I found the Sigma to be just a tad better. I think I remeber a report in one of the magazines saying that the Sigma had the edge over Tamron in sharpness. But unless you are goin to be printing really large prints, over A3, then I dont think you will spot much difference. The only drawback with the really long lense is at the extreme ends of the zoom. Some falling off of quality and possible edge distortion. Most photo editing programs can cure a lot of them though. Best advice I can offer is, take you camera along to a dealer and try both lenses. Take a couple of pics and look at them on you computer. Then you can make a personal jugement. Hope this helped a little.