Depends what you do with it. I spend most of my time doing low light shooting, so constant 2.8 beats more zoom range for me. If you use the zoom range loads, then go for that. Take a look at your existing shots, see what focal lengths you use the most, and decide based on that.
If you do go for the wider aperture, the Tamron 17-50mm f2.8 non VC is a steal. Best vaue for money DX lens IMO.