3rd party lens for Nikon D300s
I have a Nikon D300s with these various lenses, Nikon 18-200mm VR 3.5-5.6, Nikon 50mm 1.8 Tamron 90mm 2.8 Sigma 10-20mm and the Sigma 70-300mm DG macro (which I am selling). Now I want to buy a standard fast lens which I can use for weddings portraits and some landscape. The 18-200mm has served me well in good light but isn't suitable in low light situations or in what I like doing most, which is portraits. I know the 50mm is a great lens for that, but I do want a lens that I am not going to continually have to be changing. I have read loads of reviews about the Nikon 17-55mm and 24-70mm 2.8 but because of the D300s sensor size and what I want to shoot the 24-70mm isn't suitable (even though it is a great lens). However it comes down to finances, so I am now looking at the Tamron 17-50mm 2.8 VC and would like to know if there is anyone on this forum who has used this lens and how they feel about it and if there is any other recommendations out there.
Any advice would be gratefully appreciated.