I'm not sure, but I think no body but me said DEMOCRACY. It is the best governement in civ3. In civ2, it's different, with all those penalties I don't remember, but now, it is great. And I didn't mean one choose one optional tech in your game, but which is the most necessary. I already won twice diplomatic without republic, and, once, domination without chivalry but MT. The only victory that needs almost all optional techs is cultural. Especially in OCC, you need literacy (GL especially for the culture, 6 at the beginning, 12 later in the game, library) and music and free artistry and sanitation (you only have one city, better it has 100% def bonus and most tiles worked), but you don't necessarly need cavs or rifles or knights.