there are not many options for GPS for Mac, but if you use a serial port GPS unit, then a Serial to USB convertor, it will work for you nomatter what.
if you want to go a pure USB route, then there is only Rayming and Deluo that have native USB to virtual serial port drivers to work with the wardriving and GPS programs.
the last option is a bluetooth GPS, but they require batteries or another 12v car lighter hookup.
Personally, I am going for the Rayming since it has a magnetic mount and is waterproof up to 5m of water for 30min. its senstivity is -175, which is up there with some of the other GPS for PC.