To my mind, there are 15 very sure civs to be included. Which leaders would you want to see for them if there were two or more leaders per civ?
My ideas:
Americans: Washington, Jefferson, Lincoln, T. Roosevelt, F. D. Roosevelt
Aztecs: Ahuitzotl, Montezuma I, Montezuma II
Chinese: Qin Shi Huang, Mao Zedong
Egyptians: Ramesses II, Hatshepsut
English: Victoria, Elizabeth, Churchill
French: Napoleon, Louis XIV, De Gaulle
Germans: Bismarck, Frederick II
Greek: Alexander, Pericles, Philip II
Indians: Gandhi, Asoka
Japanese: Tokugawa, Meiji
Mongols: Genghis Khan, Kublai Khan
Persians: Cyrus, Darius I
Romans: Julius Caesar, Augustus Caesar, Gaius Marius, Constantine I, Theodosius I
Russians: Peter, Catherine, Stalin
Spanish: Isabella, Charles I
So pretty much the same list as in CivIV.
P.S. Numbers of leaders per civ aren't supposed to indicate the importance of the civ. I just listed all leaders I could think of.
Edit: Added Philip II