I'm a big fan of the UK version, dug it the whole way through. A solid 8.5 - 9 / 10
I only watched the first few US episodes but it wasn't watchable. I saw the UK version quite a while before ever seeing the US one, so I don't know how it would come off for someone completely unfamiliar with the series but I can't imagine it would be any different. The episodes I saw were direct rips of the UK episodes (right down to the little jokes... "I was driving a jeep." "You were driving a military vehicle?" etc.) The acting feels wooden, Keitel seems completely out of place as the guv, the pretty boy they got for the lead doesn't work as anywhere nearly as well as Simm did, and everything comes off as unnatural. 5 / 10. That's right motherfucker, 5/10. On paper you'd think the US version would work just fine given how much they share in common - but watching the US take on the series it's pretty clear the original was more than just the sum of its parts.
If you haven't seen the UK version buy it and watch it (it doesn't have a R1 release, I imported mine off of Amazon.co.uk and since I have an Oppo it played without a problem, you'll need a DVD player that can handle an R2 PAL release.)
Skip the US version either way, complete waste of time.