Most of us understand what an AI's favourite civic means. And lately, it has been included inside the GUI (nice touch firaxis) so we don't have to keep checking the civopedia. I have to confess that I never paid too much attention to a civ's favourite religion though. I know some have them because it is listed in the manuals, but even the revamped GUI makes no indication to this. I also have yet to see a discussion on how the AI's behave exactly. I guess if an AI has christianity as a fav. religion, that means you can always convert him/her to it from another, but not the othe way around? This is just a guess. I suppose depending on if they founded a religion also factors in somewhere. But I have yet to see this on paper anywhere.