Depends how you value:
(1) Local-network file transfer speed
(2) Slim-and-trim appearance
Do you have a network you'll be using this Pismo in? Do you regularly transfer large files (music, video, graphics) between your various local computers?
If you're just using the Pismo for internet access, then 802.11g speeds will make no difference whatsoever, so you might want the Airport card to avoid stubby antennae.