The "merry wives" of Windsor are the play's protagonists. (Just like Lucy Ricardo and Ethel Mertz.) We cheer on this fun-loving, mischievous duo as they set out to teach Falstaff a lesson for trying to con them and ruin their reputations.
Yeah, yeah. We know we just said that the "merry wives" are the play's protagonists, but some folks see Falstaff as the play's hero. We can't say we blame them. Even though the guy is a big mouth, a liar, a cheat, and a drunk, he dominates the play with his larger-than-life personality and his hilarious quest to seduce the ladies.
But, we think it's better to think of him as an antihero. (An "antihero" is just a protagonist who lacks hero qualities like strong morals, honesty, courage, strength, and so on. Think Will Smith as the seriously flawed superhero in Hancock or Robert Downey Jr. before he decides to be a hero in The Avengers. We don't want to model our behavior after him but we can't help but cheer for him.)