Go with the X10 or the rumored Galaxy S when it comes out.
With the x10 you can download PC Companion on your PC and you can get the latest software and firmware directly from the Sony Ericsson team. Thats what I've done and i'm running the latest firmware. My X10 is also running PSX4Droid and thanks to the latest firmware update it runs nearly perfect.
Also the X10 is a pretty sexy phone