Nikon Sigma Tamron

Nikon Sigma Tamron
Sigma or Tamron for Nikon D90?

I know that the camera I want, but the lens? I want a 18-200 but can not afford the Nikkor so it is a choice from Sigma or Tamron. 2 Sigma've seen, but what's the difference? Thanks http://www.calumetphoto.co.uk/ctl?query=18-200+nikon+fit&x=0&y=0&ac.ui.pn=search.Search . BTW I'm in the UK so please if you find a bargain in Europe, then tell me!

OS lens (first in the list) has Stabilizer Optical

Nikon 70-200mm VR Lens Review & comparison against Nikon 18-200vr