I'm certainly no expert so can't give expert advice.
But I guess any of those bodies would be good for you. However, I think that you need something that may be a bit future proof, or as future proof as can be.
If you're mentioning full frame now, I can pretty much guarantee you'll be thinking of it again in the not too distant future. So that may push you down the full frame path.
Nikon has put in place a process for cleaning dirty sensors on the D600, but it's a shame that some D600's have this problem, because by all accounts it appears to be an excellent camera. You could be lucky and get a 'good' one.
The D800 is another step up, and not cheap.
If it was me, I'd get the D600, but that's just me. It seems to answer most questions and seems to answer them well.
And Nikon are doing £150 cash back on the D600 at the moment.
http://www.wexphotographic.com/?/cashback.html&t=nikon
But ultimately, it's down to you.
Good luck.