Well, I voted for bluetooth even though personally I use WiFi more.
My reasoning is like this:
Bluetooth can do networking, although its a bit slow.
It has much better power consumption figures than Wifi, unless someone knows otherwise.
It can connect to wireless headphones to play mp3s from the SD card.
It can connect to GPS.
It can connect to mobile phones.
The last point is particulary is particularly useful given that Nokia has at leaste one phone, the N91 I think, planned with WiFi and bluetooth built in. As well as normal network conectivity this will be able to act as a gateway to wifi hotspots.
Also PalmOne has proven that bluetooth only designs can sell well worldwide, although their new PDA does have wifi.
(Personally I'm not buying another PDA till its got both bluetooth and wifi built in and runs linux!)
ltrm