I wouldn't get an XPERIA because of the custom UI. It's nice, but waiting for the hardware manufacturer to update their UI's is just loooooong. My cousins HTC Hero is still stuck on Android 1.5 lol. I believe Cliq/DEXT is on 1.5 still also.
True, Hero and other Sense UI devices are getting a 2.1 update next month, unlike the G1, but I can't imagine still not having awesome 1.6 features like Goggles, the new Market, Google Nav, etc, for such a long time.
Personally I'm waiting for the Motorola Shadow/Nexus Two. And I usually give new phones 3 months after they come out, to get them, because you can usually get a better deal by then. My contract is up in May, so I'm gonna stick with my G1 till about September-ish, and hopefully the Shadow has been out for a few months by that point.