I would prefer to get cookbooks in both formats, but to have to pick one I'd go for pbook form. Then I use MacGourmet on my iMac, iPhone and iPad to store recipes as I use them, using the iMac to load them in, the iPhone as a "grocery list", and the iPad in the kitchen to show me the recipe I'm working on.
That's the theory anyway. In practice I'm still loading recipes into MacGourmet, and often have my food-splattered cookbooks up on the bench instead.
Cheers,
Marc