I don't think it's possible to select one. They all suck, face it - humans are backstabbing, lying, non-altruistic, etc. sort of beings. Seriously, did a cat create religion? Did a frog grant oppression? Do centipedes make laws?

Civilizations are bad. However, if I were to use 'greatest', 'civilization', and 'ever', all in one sentnence, in that order, Germany, Japan, and Russia come to mind.

Germany almost took over the entire world twice (There's a lot of things wrong with that, by the way - of course, good things could come from it too.) But, in defining 'greatness' there was one such man named Alexander the Great who was given that title because he had so much land

This brings me to Russia. Overlook the actual population and any politic problems it has, but look on a map. Do you see a bigger country than Russia? This is Greatness.

Moving on to Japan, and of course tying it in to this wondrous forum called 'Eyes on Final Fantasy' what sort of people came up with Final Fantasy? Japanese people. Who was rigorous but rewarding education system? Glance back a ways and see 'Japanese people' again. Who isn't allowed to have a military - and of course, therefore pacifist/pro-life/non-warmongerring - because other nations oppress it so? The Japanese.

Once again, a civilization is a terrible thing. Especially the ones that involve people.