if you are base on UK or the forum is targeted to UK visitors, take UK domain, otherwise dot net is first choice if you can not take dot com, anyway i would rather than choose a new one for dot com name.
Definitely .net unless you were targeting the UK demographics. But yes, always strive for the .com first.
well .co.uk is for UK and .net is everyone so this is alittle unfair if you have a english business based in UK you would usually get a .co.uk more than a .com but .net is everything so of u have a global business .net is good for that...
.net is much better as it gives you universal appeal and will have you listed higher in more search engines. .co.uk limits your scope in applying to all visitors and search engines. You could also attempt to purchase the .com (if being unused) for $50-$100 from the owner seeing as how no one else owns another extension.
if you have to choose between thoos both, i would recommend .net because .co.uk is mostly based on uk people and .net is around the world...
.co.uk if mostly uk audience, if worldwide then .net, but in place of .net and how much id want the name id go for an alternative .com