wireless :whichis better usb or card insert?

I recently purchased a sierra usb aircard for my laptop. I was wondering if I should exchange it for the card (PCMCI??) that would stay in my computer all the time. Which is better? Right now my usb will lose its connection if I do not use it for 5 min or so. Some people have told me the internal card is slower. Any help would be great . Thanks