Possibly the Apostle Peter. Definitely one back when the Catholic church concerned itself with religious faith instead of political power and influence. So, on between Peter but still back in the dark ages, assuming that the Catholic church ever did concern itself with peoples souls instead of power, wealth and influence.
Martin Luther would be the best pope, but then he pointed out the fallacies of the Catholic Church and was excommunicated and didn't become pope. So the Church continues on it's path of seeking power, wealth and influence and not concerning itself with actual people or their souls.