Based on my experience with hurricanes, I'd say that D cells are in the highest demand. All those big Maglites and cheap lights clear those out. AA cells clear out pretty quick too. When there isn't a D or AAA cell to be found, there are usually a few C cells and lots of AAA cells still in stock. I've never really looked for 9 volt or lithium cells during a hurricane panic buyout, but my guess is that 9 volts sell out quicker than lithiums.

Personally, I've tried to standardize on AA cells and have several dozen AA alkalines and almost two dozen NiMH rechargables. I've sort of broken that lately with a cheap LED headlamp and an Arc that take AAAs, but they're easy on the batteries. I've got an assortment of other cell types (and flashlights to match them), but I don't depend on any of them.