Initially, I was thinking why? would definetly be my answer. As why is the only thing that really means anything, really. The rest is merely details, but why is the base for whatever it is. Then, I realized that what is very important. Why creates the what, but the what is the actual thing. Then I had to decide what I found more important, the actual thing or the reason behind it. For, truly, you cannot ask why without knowledge of the what.
I think the why is more importanty, as the why creates everything, but one must first gain knowledge of what before being able to discover the why. As such you must first ask what? and then follow it with why?
After all that, I cannot vote, as both need to be asked.
Like hewhoisdave said, a very interesting poll. It really gave me something to think about.
"Why" - because why is asking for a reason. Reasons are the base of all knowledge and power. You know what you're supposed to do from what other people (society) tells you - but if you don't know why, then you're only serving some other master/goal instead of realizing your own. "What" is merely asking for a definition - WHY do you want to know? "How" recieves an answer of process - WHY would you want to go through it? "Where" is, of course, a location, but WHY should you go there? Who doesn't matter unless you know WHY you would want to know them... The most enduring question is - "WHY are we here?" It's something that if you can't define for yourself, you don't really know, because you can't be told. Of course I also see the merit of "What" - another popular question being WTF!? Interesting poll.