Just to avoid confusion, Sigma has had several iterations of this lens. As DPReview summarized them:
70-200mm F2.8 EX APO - Original version, minimum focus distance 1.8m (1999)
70-200mm F2.8 EX DG - Addition of 'digitally optimized' lens coatings to reduce flare (2005)
70-200mm F2.8 EX DG Macro (HSM) - Minimum focus distance reduced to 1m (2006)
70-200mm F2.8 EX DG Macro HSM II - Improved optical performance (2007)
70-200mm F2.8 EX DG OS HSM - All-new design with built-in Optical Stabilization (2010)
I own the stabilized, OS HSM version personally; my office has the 2006, non-OS, HSM version. I love using both of them. The non-OS version is lighter and shorter, making it a bit more fun to actually use (My coworker keeps the older Sigma 70-200 on the office camera all the time now, but before we got it, he very rarely used the old, unwieldy Nikkor 80-200 f/2.8 it replaced). The OS version obviously has stabilization, which is a great advantage for hand holding in low light, and is probably worth the extra weight, length and money in many situations. For shooting sports though, I usually keep my shutter speed above 500, and the faster shutter speeds tend to equalize performance between stabilized and non-stabilized lenses.
I'd recommend either version without hesitation. One of the student photographers I work with owns the Nikkor 70-200 VRII, and I haven't seen any difference in the image quality--if anything, his basketball shots are usually softer than mine, but that's down to technique, not technology. The only things you miss out on by not buying the Nikon are:
1. Weather sealing (not a huge issue for indoor shooting).
2. Focus limiting (I do wish I had that, but I prefer having $1000).