Don't know if this was already mentioned, but freebies wonders have a addictional advantage.
Conquering them wont give you any advantage.
That's a huge difference in early rushes.
For example, Ramses II is building the Stonehenge. You, Alex, are building a couple of hoplites instead. Whta that means? Means Ramses isn't building for HIM, but for YOU. All you have to do is rush and conquer.
Again, you conquered Thebes and have the Stonehenge wonder. Now you start working Oracle while the enemy works for Colossus. You finish Oracle, free SP, and get the Colossus from enemy!
That said, Taj Mahal is a must have. Oracle is damn good and Sydney's Theater is awesome. Great Library is good but Porcelain Tower is amazing as you can save de GS and slingshot when you want.