The one you can afford?
AFAICR, the CF card does NOT have an extra battery in it (which is why it's "cheap").
The PCMCIA and dual PCMCIA jackets do - I have the latter, and my battery life is very good (the single has one extra battery and the dual has two extras).
Also, make sure you take all of the power-saving precautions like turning off the backlight/screen when you're not using it.
Cheers,
Refractor