Not entirely sure if thats Accurate though. Seeing as the Desktop modem comes with a massive 5-6cm Omni Antenna. Standard USB modem has internal antenna which can't be bigger than the device itself which isn't even 5-6cm.
I know in this day and age size doesn't really matter. But ye, I would take my bets on the Big-ass omni :>
PS. Pinging karoo.mweb.co.za is a good test to run (karoo.mweb is a major gaming server) I did some tests with my Desktop Modem. Pings range between 45ms and 75ms (Tested at Airport and Bellville Area)