Silly stuff like huge maps or raging barbs aside (where it is just abusing the settings), GW is one of the best wonders. You can steal so many techs with the GSpy, for a really not that huge hammer investment. And they often pay back for themselves..no more axes/chariots/archers needed.
There is just the problem of getting it on high difficulties
I would rate like that..
Mids - prolly the most powerful. If you are also SPI or PHI, this is an overpowered wonder imo.
Mainly cos the time frame to build it is long, and making use of chops beats the AI to it.
There is also the great engineer points, and you might just get all these hammers back later.
Great Lighthouse - is good but often a pain to get, cos you usually have to build it in your cap..maybe the wonder that cripples early expansion the most. But if there is lots of coast, it fixes all economy problems.
Oracle - bribing AIs into war early makes it powerful, esp. with warmongers on the map.
ToA - well...the games i built that can be counted on 1 hand

I just never seem to have time for it
TGL - lots of relative early GS points at the best possible time, one of the strongest..but this route gets sooo old after a while
Shew - mostly useless cept for fail gold, here it can be nice with gold...Philo is often bulbed, Mono is cheap, Theo or FR are usually used later
MoM - a mixed bag, certainly nice to have but often impossible to get
Taj - If you have a high production city and marble it's good, if not it usually takes too long and the usefulness of another GA decays