It's hard to get ubiased opinions about this sort of thing. Your (our) best bet is to start calling places that handle on or more of those turbos and ask them for a comparison... otherwise you will just get oooh's and aaaah's about whichever of them a particular person bought since people rarely have experience with more than one turbo of any class.
That being said, and with no personal experience with any of these, I still favor the HTB2 from what I've read. It's relatively inexpensive, spools very well, runs cool, has good drive pressures (with the 14cm housing), and is easily upgradeable, just like any other HTT setup.
The B1 has the marked advantage of being virutally indestructable, from what I've heard from people who own them, but have heard that they don't spool well, and the models that do suffer in the top end.
I don't know much about the USB line, but from what I've heard, they're 'spensive, which basically rules them out for me. :-laf