I personally think following are the best combos:
Gizah: 1. Imhotep. 2. Nebuchadnezzar. 3. Amytis
Babylon: 1. Archimedes. 2. Vitrivius. 3. Hypatia.
Olympia: 1. Caligula. 2. Zenobia. 3. Cleopatra.
Rhodes: 1. Hannibal. 2. Alexander. 3. Darius
Halicarnassus: 1. Macenas. 2. Justinian. 3. Solomon.
Alexandria: 1. Phidias. 2. Praxtelites. 3. Berenice.
Ephesus: 1. Croesus. 2. Xenophon. 3. Midas
However, this is just the best picks. For example, all the one coin leaders provide a cash boost for your board. The two cost leaders are varied, each with their own power, but Hannibal is undoubtedly the best by giving you age 1 victory.
Of the three cost leaders, Nefertiti, for 4 points, is better than many people. Alexander demands you to win almost all your wars, Aristotle requires to amass two science sets, Midas needs you to end the game with at least 15 coins, which is difficult and meaningless. Hiram demands you spend over a third of your age 3 picks on guilds, assuming, they each generate you at least 5 or 6 points each. Praxtelites needs you to collect every manufactured resource (glass, cloth, paper), assuming your natural production is not a manufactured source and your neighbours don't already have one. Aspasia gives you two direct points and a peace to prevent you from losing two, so Aspasia is bascially Nefertiti's long-lost twin sister. Unless grabing a vital science crad at the start of age 3, how often can Solomon give you a card worth 5 o r more points? The best age 3 leaders are Phidias and Varro, because resource and commerce cards are cheap and necessary for most people. Caligula can let you build powerful cards for free, such as capitol for 8 points, or contingent to let you win age 3, so he is good. Justinian seems difficult, but if you play him right, he can generate at least 9 points.
Among the 4 coin leaders, 3 beats them all. Archimedes, Bilkis, and Tomyris. Plato, on the other hand, sucks, and so does Amytis, unless you're paying Gizah B or Great Wall of China.
Among the 5 coin leaders, they go to extremes. Caesar is good to recruit for war buffs, and has the same power as militia, but costs 1.6 times as much, so unless I take someone like Macenas or Nero in age 1, I'd never recruit Caesar. The science leaders should only be played at the start of age 3. If one completes a chain, it has earned you at least 8 points. Ramses, on the other hand, gives you free guilds, but it depends on what your neighbors have and whether or not guilds are worth it, compared to military, science, and civilian structures. Hiram and Ramses go hand in hand, but is normally, like Caesar, someone you don't want to recruit. I'd always desire Hannibal or Varro over Caesar or Hiram.
Finally, Pericles is the lonely 6-coiner. He costs a lot, but generates 2 vp for every red card. So, if you lose in age 3 against both neighbors, and wasted so much money on 4 red cards. Your net gain is actually 1+1+3+3+(-1)+(-1)+(2*4)=14 points, which is the equivalent of taking 1,3,5,5.
So therefore, my favorite 5 leaders among all others are Croesus, Hannibal, Justninian, Archimedes, and Bilkis.