It's a laptop: get PCMCIA.
The speed is thesame except with USB you have more control over where your antenna goes.
Since you have a laptop you don't want to lug around a gigantic USB cord with an adapter dangling over it.
If you had a desktop...USB. Because (1) Desktops don't have PCMCIA

(2) You'd have to get PCI, but there's a chance of IRQ conflicts and (3) the antenna might get in the way of your hot 5.1 surround setup wires... or any other wires (Monitor, etc) - less freedom (or should I say no freedom, except for changing PCI slots) to position your adapter.
Edit: You mentioned it was a stationary laptop. I'd still get PCMCIA, because AFAIK, laptops generally don't have a ton of USB ports. Might want to save those

.
-TPG