Wow, I did not expect to see a carrier carrying the Sonim XP3, that phone is a complete brick nor did I expect a carrier in the USA to carry the Motorola XT720.
I have the XT701 that I got from Hong Kong. It has quad band GSM and tri band 3G (850,1900 and 2100mhz) and works perfect for AT&T. Unlike my Milestone, the XT701 was able to find AT&T's data settings on its own and locked them in. With the Milestone I had to enter the APN settings in manually. It switches from 3G to HSDPA depending upon location. The phone is a bit quicker then the Milestone.
The camera is quite awesome and the Xenon makes the difference. The battery cover is metal like the Droid and Milestone and the phone uses the same battery as the milestone/Droid.
The odd shape of the phone is not that bad and also acts as a way to keep it from sliding from your hands when carrying it.
The back of the phone has a distinct metal feel to it unlike the Droid/Milestone with their rubberized metal backs. The trim around the sides is metal.
The one thing I don't like is not only do the side buttons wiggle but when you shake the phone they rattle. It is a Moto design error. The Droid and Milestone side buttons also wiggled but did not rattle. I have no doubt that the buttons will work for a very good long time and I will get used to them quickly but for you OCD types it might bother you.
All in all the XT701/XT720 are good phones.
As for the Nexus 1, I did not like the track ball as it was a bit touchy and sometimes it did not register and you had to click again. That may have just been my phone. The big thing in the N1's favor is that it should be the first to get Android updates each time around.
The HTC I know nothing about as I don't like HTC having had several horrible HTC phones and I gave up on the brand