My tier list is going to have to be:
1. Maya. They're incredibly versatile, as has been repeated ad naseum. Their ability to do whatever they want thanks to easy religion and boosted science, makes them the best civ, IMO.
2. Korea. Wow. These guys tech like there's no tomorrow. Sure, they need universities to really get into their stride, but they're incredible afterwards. They're superior to Babylon by a country mile. This is because due to escalating GP costs, not to mention that a good half of your GPs will come from sources other than naturally popping them, means that at most, their boost provides rt150% of the scientists of other civilizations. This is 122%, or a bit over a scientist a game. The early GS is great, but I'd rather have 5.33
/city in boosts at Education than 8
/turn at Writing. Ten cities, assuming half have observatories, makes that a 45.33
/turn bonus at Education, as opposed to the 10.64
/turn provided by the Writing GS. The early GS is lost in the snowball. The extra GS later, too, is completely lost by endgame. Also, that's not even going into their bonus science from buildings and wonders in the capital, each of which is half of a research agreement. The UUs are gravy.
3. Inca. For reasons I need not restate, as they have been explained to death in this thread.
4. Ethiopia. They're arguably the best at Deity, but this is a list for any level. The bonuses are great, blahdeeblah.
5. Arabia. The ability to double luxes with a beeline that fits in nicely with their desert start bias, gain a tremendous amount of GPT from trade routes when ICSing, and a god-tier UU make this an extremely strong civ. The doubled Oil is nice, but not really necessary with such a wide desert civ.