Hi I hope you can help me.  If this is in the wrong section, please move to the right one?  Thanks.

I’m looking at two lenses:

• Sigma 18-250 £319, (reduced down from £329)
• Tamron Dii PZD 18-270 £270

I would like to buy one of them. At the moment I have a 18-105 lens which has done me well, but when I had my Pentax I owned an 18-200 lens which I liked.

I do landscapes, but also costume jewellery and portraits (occasionally) Please can you tell me which is the better lens to go for?

Thanks.