Tamron SP AF 70-200mm F/2.8 Di LD (IF) MACRO or Sigma 70-200mm F2.8 EX DG OS Macro HSM II?

I need fast lens and good for low light activities for my Nikon D3100, i know that 70-200mm Nikor is good one but it is super expensive for me. So I'm planning to get cheaper one with price range of 700$.

I would caution you. Cheap means exactly that - cheap. Buy cheap and you'll get cheap.

I have one Tamron lens and I won't have another. It has focus and aberration issues so it now lives in a drawer in my office never to see the light of day again.

Most of us regulars here would recommend you buy Nikon lenses because of the glass quality and over all high quality level of the equipment. More expensive means higher quality.

Take a look at these lens tests:
http://the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx
Contrast looks better on the Tamron at long end
Better on Sigma at mid range

Tamron looks better overall but consider Nikon as well