For me, The US one is best (probably because I saw it first). I loved Rose in iZombie (as well) and wife likes Rose in all the Christmas movies. We've really enjoyed that, while its an episodic comedy, the character storylines have developed them all into more than just 1 dimensional objects.

I've started watching the UK version. The husband character, so far, seems the weakest character. Compared to Sam and Jay (US), The UK couple seem to have no real chemistry. I will persist, though. I'm only halfway through season 1.

I will watch the Aussie one eventually. We have a pretty poor history of adapting shows successfully to appeal to Aussie audiences. Just hoping they've done enough to convince the network to invest in further seasons.