UIs are a really personal thing. Something one person loves another may hate. I can't say I have any experience with the Moto UI, but coming from Samsung and Touchwiz I really like the LG UI. I think it's very nice with lots of options to customize to personal taste.
Regarding updates, there's no way to tell, but here's how I'm choosing to look at it right now ...
This was a big phone for LG. You can tell that they put a lot of effort into it, likely to try to gain some market share back from Samsung. As such, I feel like they may use this phone as a platform to try and beat their Korean competitors at every turn, including getting OS updates out faster and cleaner. This is just a gut theory of course, and from what I understand, LG isn't exactly known for their speedy OS updates, but I still remain optimistic.
We shall see.