I had Gold first and later got C3C.
The default game is PTW. Medieval Infantry were added in PTW, as was the ability to move similar units out of a stack. That is, in a stack of 30 units, with 10 workers, 10 spears, 5 swords and 5 archers, you could select and move all of the spears at one time, leaving the other 20 units in place.
Also, in PTW, Ring City Placement is important and so is the placement of the Forbidden Palace.
So, if you have Maces in your game, you have PTW.
If Korea, Spain, Scandinavia, Celts, Ottomans, Carthage, Arabs or Mongols are in your game, you have PTW.
C3C can be found on eBay or Amazon for around $20 or so. Get it. Don't bother with the Conquests expansion. C3C installs all 3 versions, but defaults to Conquest. Also, in C3C, each version has the latest patch in place, so you don't need to do that updating manually.