Wireless adaptor

Depends on your router -- if you have N router get N wireless adapter from same brand.

On a more general themes -- if choosing between USB and Pc card -- go for card.
Brand wise -- I've found that most, even the cheapest no-name models, work pretty much equally -- no surprise as they all use the same small pool of chipset manufacturers. Difference is in support - buy a big brand and you can expect continuing driver and firmware updates.