The Nexus line is the logical choice since they are unbranded, so there is no need to wait for AT&T to update their crapware after a new Android release - there is no crapware to begin with. The Nexus S was the first to get Gingerbread, followed quickly by the Nexus One. Google intended them to be developers phones.
There is no Nexus 4G out yet, but specs are out there and it might be due around Thanksgiving.
http://www.bgr.com/2011/06/15/exclus...e-android-4-0/ (There is a Nexus
S 4G available for Sprint)
I've seen new Nexus Ones going for $250 if you need something quickly and can live with 3G for now.