Which one to go for?

[Nevakonaza]

Kona Lanai 2011
http://www.evanscycles.com/products...ium=affiliate&utm_campaign=awin&promo=Content


Mongoose Switchback Sport 2011
http://www.evanscycles.com/products/mongoose/switchback-sport-2011-mountain-bike-ec026625


Carrera Vulcan V Spec
http://www.halfords.com/webapp/wcs/...2_1312984122_b0c475378fc297ca4826ebe54ee838de

So far these 3 look good to me,My max budget is £280.

appreciate the help.