Domain name choise for SEO

Hi Guys,

I am about to start optimizing a website of a UK based company,
which has two following domains:

www.thekitchenstudio.net PR3
Creation Date: 29-aug-2001

www.thekitchenstudio.co.uk PR1
Registered on: 23-Feb-2004


Which domain would you recommend to optimize and why?

Thank you,
Polly