I have tested both, and they do exactly the same, with one exception, there's no disqec control on the USB ( as pointed out by Rolfw.) The only advantage with a USB is that its portable and it works on laptops. The Technisat software is a different one for each, but use either DVB Dream or ProgDVB in just the same way. See http://www.sa-computer-systems.com for easy instructions
I'm not sure about 4:2:2 but I know the USB versions cannot be used for HDTV reliably since the bandwidth of USB is not enough for the HDTV MPEG2 stream to be passed back to the PC via the bus. As for the best deals, Skystar 2's often turn up very cheaply on eBay or, if you don't mind waiting, www.dvbshop.tv have a good reputation for being cheap and reliable.