I think PCI-e wireless cards have a higher data thorough rate than USB, so I would recommend PCI-E, but if you dont want the hassle of installing a daughter-board into your system, USB is the way to go. If youre going with USB, try getting USB 3.0 if you can find them, their data rate is around 5 gigabytes per sec., USB 2.0 is much slower
Also, keep what ForgetLavender said in mind