There are certain series where the question “Which one’s the best?” is difficult to answer. Ask someone what their favorite Civilization is for instance and you’re bound to start an argument. (It’s Civilization IV, by the way.) The same goes for Mario, Zelda, Final Fantasy, Fallout, Smash Bros., Mortal Kombat, Tony Hawk, Assassin’s Creed, Street Fighter, Elder Scrolls, and so on and so forth.
Age of Empires? Not so much. People by and large consider Age of Empires II to be the pinnacle of the series. Oh you might find a few holdouts for the original, or for Age of Empires III, but the second game is the runaway fan favorite—as evidenced by the fact Microsoft remastered it back in 2013, before the original.