Advice on lenses: Sony 55-200mm or Sigma 28-200mm?

Hi,

I am new in DSLR photograph and just have A57 with kit lens (18-55mm).

I want to buy a used lens to provide a wider focal length. I would appreciate advice on the following trade-off:

At first I was thinking on buying the Sony 55-200mm to combine with my kit lens.

http://www.dyxum.com/lenses/Sony-AF-DT-55-200-F4-5.6-SAM_lens522.html

When searching for used lens I found in the same price range ($100) a  Sigma 28-200mm, which will give me the wider focal length + mobility to carry just one lens since it starts in 28mm.

http://www.dyxum.com/lenses/Sigma-28-200-F3.5-5.6-Compact--Aspherical-HZM_lens138.html

Considering some reviews, it seems Sigma 28-200 performance is worse than Sony 55-200mm. But since I am a newbie with low budget, Sigma is being very attractive.

What is your opinion? To whom have begun with low budget, what would be the best way to go?

Thanks in advance,

Cadu