Flashes that use 2 AA cells vs. 4 AA cells

Just wondering what the pros and cons are for flashes that use only two AA batteries as opposed to four. I remember using an old Vivitar 3500 that used two AA's and they didn't seem to last too long.....Is this the case for all flashes? I'm about to decide on getting the Speedlite 220EX (uses 4 AA's) or the Sunpak PZ40X (uses 2 AA's) to use with my G6.

4 battery vs. 2 battery comes down to these three things:

1. Quantity of flashes per set of batteries
2. Speed of flash recycle
3. Maximum flash output power (called Guide Number)

It all depends on what type of photography you are doing and your budget.

This would be general shooting, little macro work (mimimal power consumption), and not at the extremes of the flash range limit. The PZ40X has about 30% more power than the 220EX. Of course, the Speedlight would be lighter due to the fact it only uses 2 cells instead of 4.

If the Sunpak does have the fill-in flash ratios (controlled either by the G6 or the flash), that would put it in the running as the first choice.

I need more opinions!