I use an iTrek M7 combo unit and find it as good as or better than any other GPS receiver I have, Bluetooth or USB. I have tested the USB in XP and Vista and each can load a suitable driver without using the install disk. Battery life seems good and it has an option to change from 1Hz to 5Hz signal (I haven't tested this but others have). It also works fine with the Vista Bluetooth stack as well as the Toshiba and Widcomm stacks on XP.
I have not tried any other combo units though so cannot compare it to them.
Terry