If you're a UK business with the UK as your sole or primary market then your "best" domain will be a .co.uk (read Nominet's business research reports, now in their 6th year I believe)
If you're aiming at a global market then .com is key.
All - and I do mean ALL - other extensions represent one compromise or another, and take you further away from the ideal. This is as close to "fact" as you can get in our industry.
I would have hoped in 2012 the above would be a "given"! .
Whilst it might be a given that often it is better for UK businesses to have .co.uk domain names over and above other suffixes, this is for various reasons. Just because it may be better for UK businesses to use the co.uk suffix that does not mean a co.uk domain name will win on exact match when it is up against a .com, .net, .co or other suffix that has been developed better, optimised better and established longer.
I think things are continually evolving and my view is that the domain name industry has to be ready to adapt to changes as more and more money is put into development within the digital arena as it is the increase in the production and development of sites that will ultimately lead to an increase in domain sales.
Proving to end users that the domain has value in development terms is one of the things that is likely to increase the flow of sales – and with this I believe many things need to be taken into account such as age (the older the better), monetisation potential, and phrase match because phrase match acts as a good guide for build out potential.