List the five leader/comanders who you feel have most significantly contributed to our knowledge and understanding of how to conduct war
That's not how I rate generals though, I see your point, but I consider generals based on their talent and performances depending on the factors against them. In regards to the above I consider what you might call "the art of war" to either be far to generalised to be attributed to any one person, or far too specific to one period to be useful to another general. Whatever Napoleon did or did not write down, whatever Caesar and Alexander did, I consider their contributions to be of little overall value to anything either outside their period, or to be very much a case of common sense to begin with. Much of what Napoleon codified was nothing especially new or especially brilliant, and whilst you may wish to attribute genius to those facts, I rather prefer not to. The essential problem with labelling genius based on the art of war theory is that it relies more on the General's reputation and people's knowledge of him than it does his actual talent. All 3 of those you mention are extremely good soldiers and commanders, however, I don't personally consider brilliance to be based on an ability to write down what has almost always been practised, or to publicise his abilities better than others.
Exactly my point! Do you know who conducted the second human heart transplant? Is that person a worse heart surgeon than the first guy?

Warfare changes, only the blindingly obvious remains the same. The talents of one general cannot IMO be removed just because someone happened to be a very capable general hundreds of years ago. The situations of the past are of use to the present, but ultimately, it must be for each generation to provide it's own rules on war outside of the textbook theories and studies of campaigns that may not be relevant to the situation.
So in that respect, I have no list two. Alexander etc were extremely good generals, however, their ability to teach the modern period about anything the modern period can't figure out in the first place from common sense is to me limited. I've not really thought about an overall top ten either as I prefer to divide it into periods. One commander may have been extremely capable at his time, Napoleon for example, but in another time period, with armies more rigid and a moral code less free his performances may have been much worse. That's why I move away from sweeping the whole of history as I don't believe that one man can transcend the entire history of man and have such an impact.
Of course all the above is just my personal take, each to their own naturally
Co-incidentally, if there's one thing I definately admire Napoleon on, it was his ability to run an empire from one man and his attention to detail. Cynics claim that a quick word with the Regiment's officers helped his "memory" of his men of course, but given his rather remarkable ability to deal with Minute detail whatever the subject that seems unlikely. Then again, Napoleon's style of government and situation enforced this in a way.
Just reading an excellent book on the 1809 campaign at the moment. What's remarkable is the stake he placed on events there and what would have happened had he failed. Had he fallen at Rattisbon rather than be wounded slightly his army, campaign and state would almost certainly have been lost. Or had lost Wagram as badly as he did Aspern Essling for another example, just how badly that would have damaged his position. As he himself said, (roughly, I'm paraphrasing

) he ruled by victory, glory and fear, lack of any destabalised his position.
Oh and on comparing the two (Wellington/Napoleon)... well Napoleon once did apparently. When first hearing of Wellington's skilled retreat before Massena in 1810 he remarked "My god! there is a man for you" and concluded by admiring his ability to retreat before a larger army and still inflict punishing losses at every turn. He concluded saying "all of europe, only Wellington and I are capable of carrying out such measures". Rare praise indeed from Napoleon.