You could easily start a thread on each of these ten points. Anyway:

1) The Greatest General
Hannibal. Unoriginal, I know. But he's just so extrodinary.

2) The Greatest Army
The Mongols. They didn't have an army, they were an army.

3) The Greatest Campaign
Alexander.

4) The Greatest Battle (tactics-wise)
Cannae.

5) The Greatest Battle (purely for heroics)
Battle of Britain.

6) Greatest Rivalry
Rome vs. Carthage. Because it was a rivalry that was fought for the very existence of either.

7) Biggest Upset
Japan beating Russia in 1905.

8) Most glorious victory
Joan of Arc kicking English but.

9) The Worst Error
Napoleon and Hitler invading Russia.

10) Your favorite area of military history
None in particular.