The UK one was better.

I watched the UK one first, after watching the pilot of the US one I thought it was going to be an awful imitation of the UK one (despite having a good creative team and Gervais' input). But as you suggested, the US one certainly comes into its own really well.
The UK one is awkward, cringed worthy, and dark with a very bleak outcome/outlook. The US has great awkward comedy and even some dark humour at times, but the biggest change is how the overall tone has a sense of optimism to it. The US Office will have a character fail, but eventually there will be a silver lining or something positive in the long run. The UK Office will have a character fail and that's that, no one would care for him.
After initially preferring the UK one, I started to lean slightly towards the US one for my favorite of the two after it's 4th season.

This message has been deleted.

Cheers mate, I'll probably it give a go, mate.
KR

Yeah mate, it's quite a fun ride, I watched the US version first and I'm now finishing the UK one but let me tell you, both are great series, the US has a lot more comedy, characters with much more depth (since it's longer) and Michael Scott (Steve Carell) does a great job as the protagonist, the UK one is a lot more cringy, awkward, even stupid as a whole but seriously funny. So yeah, give it a go mate.

I've been told the exact same thing so I decided to give it a go, it looks good I suppose but I couldn't get past the fact that it's literally word for word and no where near as funny. But I will get through season 1 and see the rest.