[jpsum]

Both are Sigma lens for Nikon.

1. Sigma 17-70mm F2.8-4 DC Macro OS HSM
2. Sigma 18-50mm F2.8 EX DC HSM Macro

Lens #1 has Optical Stabilization but Lens #2 has a constant aperture (2.8!!!). They are both around $400.

I really like fast lenses so I'm leaning towards the 18-50.