I went with USB because there were more places to use it. I have a Cradlepoint travel router and actually bought their larger router for home the MR 1000 for home. When the device is not on the road, I leave it plugged in as a back up at home.

I really love the portable router because there have been too many times that I have had to put the modem in a place I didn't want to sit to get the best signal (e.g. in a window or once in the bathroom). I bought a cigarette adapter for my Cradelpoint and have on more than one occasion used it in the car on the road.

The Express card version certainly looks cleaner and most of the time is little bit less in the way. Conversely, I have only one Express Card slot and three USB ports.