With USB you can get a longer USB cable to attach the USB wireless adapter to. If the signal is weak you can move the USB adapter on the extended cable to where the signal may be stronger without having to move the laptop or move around in the room looking for a strong signal.
I've even had to hang one out the window to get a stronger signal.
The down side is that most peripherals now come with USB connections. Depending on how many USB devices you use, and how many USB connections your computer has, taking up the USB connection with wireless may be a problem.
hth DDS W 2k MVP MCSE