Buying from Steam, us or euro version?

So I downloaded a US trial because I was told the European servers are pretty much empty. And now I'm thinking of purchasing the game. Steam has a sale right now with a good price. Thing is, I live in the Europe. If I buy the steam version, does that mean I can only play on European versions? I'm guessing that the steam version when buying from the UK is a European version see. But does that matter or how does that work? Do I have to try and get an activation code from a US version or does any version work since I've got a US trial version?

Unfortunatly, steam is locked to your region (unless gifted a game from a friend in a different region, sometimes that will give you theirs.)

US versions can be bought from the PlayNC store, or possibly just upgraded from your account page, although you miss out on the -33%, and with the current exchange rate, its a fair difference between EU on offer, and US at normal price.

But, on the other hand, the EU servers aren't dead from what i hear, and are comparable in population to the non-highest-populated US ones. Only difference being that you will not find people on at all times of day (as with the larger few US servers), pick up groups can be a pain to find (easier if you're the one organising them, as not many want to lead), and the general consensus from EU players is they feel like they do not get adequate dev/support attention after the EU office was closed, and they are now part of the larger single community.
They're not everyone's cup of tea, but you may find a home there if you decide against the US.