One golden age per game.
In my opinion, the best golden age would be a middle ages one, while you are building the Sistine Chapel and Sun Tzu, and researching toward Copernicus. Nailing those wonders will give you a nice edge vs. the AI, and the golden age all but guarantees you will get them. As the Egyptians, a civ I've been playing a lot lately, build the Great Library, not the Pyramids (I don't recall EVER building the Pyramids... the GL is much more important to me). Use your war chariots to spark the golden age (leave a couple of them lying around, upgrade everything else to better units like Knights, pick a fight, and whack a weak enemy unit with the chariot).
When I play the Babylonians, I tend to spark golden ages by building the Great Library and Colossus. If the Colossus comes late enough, then my golden age will be on time. If not, it may be a bit early for my taste.
In general, I think a golden age really early, while you are despotic, is a waste. This is why I've yet to force myself to try the Aztecs. The later the golden age, the more powerful it is. However, the reason I like the middle ages golden age is that there are so many key wonders of the world there (Sistine, Sun Tzu, Copernicus, Newton, Bach).
-Arrian