I have purchased a Dual PCMCIA Sleeve for the iPaq, I also use CF cards with it, with a PC Card Sleeve you can use both. Also if you are using a CF adapter in the PC Sleeve, because CF cards draws so much less energery the fact that they have to use battery is kind of irrelavent since you would not be using that much. If you plan on upgrading in the future to wider ranges of devices I would recomend a PC Card sleve, sometimes they're a bit bulkier but more compatible.
For example you can use just about any CF Card with a PC Sleeve, and the PC Sleeve ( least the one I got from compaq) comes with a CF adapter.
you can use PC Sleeve for storage via CF card, or even buy PCMCIA harddrives upto 5 Gigs. Also PC cards are not limited to network connectivity, they can be used for a very wide range of devices, more so than CF are currently found in.
But depends on your preference.