As for the WP8 UI being beautiful, like someone said....its preference. I never liked the minimalistic themes and ROMs Android has available. The fonts changing in JB for the notification shade kinda caught me off guard. And I dont think the Live Tiles setup is as functional as widgets. If they were available on more than one page, then yea. Then the information in the Tiles are all contained in a tile...it just looks too similar for my liking. I like the uniqueness of some widgets.
Just personal preference, cuz I know some ppl love the minimalistic themes, ROM on Android. Some love the WP themes available.
As far as smoothness, lag...I started with Android 2.0.1 on my Droid 1. I have a Maxx HD running a JB leak. Google has been addressing smoothness n lag with every Android OS update. Is it as good as iOS? IMO, Yea. WP? IMO, No. I still think WP is the smoothest, most lag free mobile OS out right now. Will Android ever be smoother, more lag free than iOS and WP? Who knows. Depends who you ask. I personally have no issues with smoothness or lag.....especially because I started with 2.0.1....have personally experienced the progression to JB and I still have that on my Droid 1 for reference.
I would be glad to lets folks borrow my Droid 1 and then we can talk again about what you think about smoothness, lag.. lol.
Stability...I dont know what to say. I have had less crashes and random reboots on my Razr from last year and Maxx HD vs my Droid X1. Better hardware or software? Dont really know the reason. But so far....Android has gotten better over the years, not worse. So unless Google decides they just dont care anymore.....it can only get better.