Is Tamron 70-200mm f/2.8 VC worth over Sigma 70-200mm OS ?

Tamron is more expensive, but it is worth it? I am mostly interested in f/2.8 shooting at longer focal lengths >100mm.

I would rather choose Sigma if it performs (f/2.8 sharpness and autofocus) similar to Tamron because it is cheaper.  I am a nikon user so the only brand alternative for me is the old 70-200mm VR. But apparently it is very bad at corners... or is it? How does it compare to Sigma and Tamron?

Any thoughts? Thank you!