Oh... If you want to be able to get the HIGHEST signal strength, a directional (Can, Yagi, Helical) Antenna will do... If you want to be able to pick up APs from all directions get a Omni-Directional antenna (like the one you linked to, however there are ones you can build)...
If you want to show off a ghetto antenna, build your own. If you want something that looks like it was made in a factory, buy one. If you want something that looks custom made, build your own but put *alot* more time into it. I'll see if I can pull up some homebrew antenna sites (pretty much just searching around google).
Edit: I just looked at the price on that antenna you linked to... that looks like a pretty good deal... If you want to be more inconspicuous and want to use an external antenna that could be a possible choice...
PS.. Some wireless hardware that have multiple antennas use one for sending and receiveing signal and the other just for receiveing *or a combination*...