This is a no brainer. If you have a holy city, or expect to found a religion later, shrine... followed by an aggressive missionary program. Do all of this early enough and if circumstances permit you could end up with 1 or more AI Civs converting their entire civilization to your religion. +5 Culture, +1gp per city with your religion, and of course the intelligence gathering. You get one Great Prophet odds are good you'll get another one later on down the road that you can use as a super specialist. Shrine first, shrine always, no way am I even going to consider giving up that much potential cash. Before being so hostile you might want to remember that your religion can be easily spread to other Civ cities.