Johnny Unitas was the best QB in Colts history because he was inducted into the hall of fame in 1979. He was a 10-time Pro Bowler and 5-team First-Team All-Pro. He threw 40,239 yards and 290 touchdowns which are records in the Colts team history. Since this question is asking for an opinion than you have to mention one other QB, Peyton Manning. Since he is still active his career numbers are not really up there with Unitas's, but he's a 3 time MVP and a Super Bowl Champion. When he retires he will certainly go the HOF and will certainly be considered one of the best QB's of all time.