Pericles had my vote, because Creative and Philosophical has been great combination from the start, and even greater it is now, when Creative has bonus to Libraries and Greeks have Colosseum-based UB which is clearly better than Mayan Ball Court, for example. If the rumors about Phalanx-units being now Axeman w/ March are true and hill bonus maybe remains, Pericles will be the ultimate leader before Medieval era. If Greeks can survive through Medieval, Pericles will probably win many, many games by outteching others.
It's funny, because I was about to make a thread which had the purpose of moving the Greek UU to an axeman replacement, with +25% hill defense and Formation for free. Then, I decided nobody would go for it because there were already two new axemen UUs, and only one new spearmen UU (Holkan).
The Greek UB is one of the greatest in the game: an additional +3 culture, +1 happiness from hit singles, a flat +1 happiness, and enables artist specialists? Wow! Babylon only gets +1 health!