Personally hate the UK One. I have it on DVD - and there are some very funny moments, but most of them are just cringeworthy and embarrasing.
The US is unintentionally funnier because they just don't really get subtle humour.
Perhaps some of the UK office is stuff that you see every day (That isn't really particularly funny) whereas the US is a glimpse into a different mindset and it's interesting to see that all Americans aren't all "Yay!! Yay!! Yay!! Yay!!" about their companies ideas (Which is how they are usually portrayed)
The UK one is supposed to be mostly cringeworthy and embarrassing to watch.
I don't think it's fair to say the US one is unintentionally funnier either - it's written to be more of a 'sitcom' with obvious gags and much less of the subtle, cringeworthy stuff in the UK one. Partly because it doesn't translate as well - like when Michael pretended to fire Pam, and started shouting "YOU GOT PUNK'D!" at the top of his voice. He came across as an arsehole whereas when Brent did similar, then realised he'd fucked up and tried to downplay it, he came across as an idiot who was just trying to be funny and make people like him.
Not sure I agree with your last point either. The mundane, everyday stuff the UK version portrayed wasn't meant to be 'funny' in the haha sense, it was meant to be funny because people would recognise what went on; the boss that wants to be everyone's friend, the co-workers that constantly grate away at you etc. Whilst the US version uses those things as a jumping off point they go completely over the top - whilst Jim and Dwight are based on Tim and Gareth they're caricatures of them - they're exaggerated for the sake of the joke.
I don't think you can say which one is definitively better - I like them both, but they should really be treated as completely different shows, with different styles and goals in terms of what they're trying to do to the audience.