The below chart from reddit user reddit_user_1948 interestingly shows how many lines each of the original 6 Avengers have in the 3 Avengers films and Captain America Civil War.
Iron Man has the most lines of the heroes, even in the Captain America led Civil War. Black Widow’s lines seems to have dropped with each new entry. Hawkeye surprisingly has more dialogue than Thor in Age of Ultron, by which point Thor had 2 solo films.
What do you make of the data?