Kinda surprised to see Petra didnt make final 5. It's pretty much the only wonder where if you get it right (particularly in capital city), it's game over. Of the remaining 4, Colosseum and Forbidden City are clearly the best, as both significantly better your position. Big Ben is good too, but wildcard slot is notably better than economic slot, and by the time you would get Big Ben, gold really shouldn't be an issue. Great Pyramids is nice, but AI often grabs it before you can at higher difficulties and I think workers often don't come into play in a big way until mid game.
If I had to choose between Forbidden Palace and Colosseum, 7 times out of 10 I probably take Colosseum just because amenities/happiness/culture are so strong at the point in the game where it comes in.
Thus:
BIG BEN = 15
COLOSSEUM = 12 (11+1)
FORBIDDEN CITY = 23
GREAT PYRAMIDS = 18 (21-3)
Moderator Action: Fixed Great Pyramids vote count --Jon