If you get an active antenna, make sure you wire up the 15L so that you're giving a good clean 5v to the antenna bias line. I forgot that part and have to go back and add an LM7805. I'm using a Maxrad combination GPS antenna/NMO mount, it's designed to be active but it seems to work fine running passive.
The stick antenna is a quad helix, the flat pancake is a patch antenna. Patch has higher gain straight above, quad helix has higher gain towards the horizon. It looks like most vehicle antennas are patch antennas. See http://www.tessco.com/products/displ...h=false&page=1