I've used the X10. Unfortunately, SE managed to take a good mobile OS and throw a wrench into it.

What's there of Android is good, but everything SE does just makes it worse. Media and social networking apps that are too slow and don't show enough info; a keyboard that's unreliable and makes the stock keyboard seem intuitive; and of course, it's stuck on Android 1.6 and won't get 2.1 until after 2.2 is old news.

I wish more companies would realize that some just want the most recent features and a no-nonsense UI.