I don't think you mean popular, I think you mean recognized, and I think the answer to that is directly proportional to the size and influence of the country they represent--with the exception of the Monaco royals who have great recognition because they essentially represent a "celebrity/jet-set" life and their mother was a hollywood star (indirectly they represent the USA). For example, Princess Mary (and the family of Denmark generally) is popular among Royal Watchers, but I doubt that the average person knows all that much about the princess or the royal family of a country with no more than 5 million people and an economy that's maybe 24th or 25th in the world, versus, let's say, a British Princess who represents a country with over 60 million people and the 4th economy of the world. Once William weds his wife will be the most recognized in the world. Right now the most recognized are without question the British Princes and the Grimaldi family, followed probably by the Spanish. Even the most beautiful Princess of them all--Sweden's--is probably not recognized much beyond her natural sphere of influence. Maybe some day one of these Prince's or Princess'es will break out of that natural order, but I don't forsee it happening anytime soon. Because, for example, Abdullah and Rania didn't become well known world wide by sitting in Jordan and doing their thing, they've made an all out PR effort to be seen and known throughout the western world. I don't see any one else doing the same thing.
But I just have a much smaller sphere of influence.
