B J Hunnicutt!
Such a wholesome guy, adored his wife and didn't do nearly as much womenzing as Trapper or Hawkeye, he just seemed like an all round good guy when I watched it as a kid.
Raydar and Charles are close seconds, Raydar because, well hes Raydar how could you not love him, and Charles because he was a good breath of fresh air compared to Frank and played off against the others really well, also changed the dynamics of Houlihan, it wasn't always her and Frank against the others any more, she had the odd team up with Hawkeye working against Charles, I like feel he bought a much better balance to the show.