Nikon 55-200 VR or Sigma 18-200mm? Which one is better?

I am using a Nikon D3000. I would like to take portrait and landscape pictures with a good quality. Which one is better? Sigma 18-200 is much more expensive than Nikon 55-200 VR.

Read more: Nikon 55-200 VR or Sigma 18-200mm? Which one is better?