I think the title says it all. I'm personally in the market for a new Windows Mobile phone and this video covered the four phones that I'm interested in.
The video is about 8 minutes long and gives you a pretty good feel for the sizes of the devices.
All four phones are Windows Mobile Professional Devices and all four have high resolution screens. The Touch HD and the Experia have a screen resolution of 480x800, the Diamond and Diamond Pro have a resolution of 480x640.
If you're shopping for these phones you may want to keep in mind that there is better software support for VGA devices (480x640) than the WVGA devices.
Also a key feature (or lack of) on the HTC HD is the lack of a directional pad. This means you're going to be controlling everything using the screen, it also means many games will be unplayable. However for a device this cool you may be willing to overlook it.
I'm currently leaning towards the HTC Touch Diamond - I'm ready for a small and "cool" phone.
As always, if you're looking for software for any of these phones check out
http://www.wireless-gaming.com & http://www.wireless-apps.net in the Windows Mobile Touch section.