Ray and Clayton are my choices.
Ray is one of the 4 Ewing boys, and one of the only 3 that appear regularly. He's the foreman of Southfork, he's Bobby's best friend as well as his older brother, and Ray is an interesting character because he grew up in very difficult circumstances: Imagine growing up in a small town where everybody knows that your father is the town drunk , Amos Kreebs - a total loser! He goes from having a father like that to having such a great, heroic man as Jock Ewing be his father and it changes his life - for the better! Ray was incredible during the Mickey Trotter storyline - possibly Ray's finest performance.
Clayton is amazing because he, in a way, sort of replaced a man who was practically looked up to as a God by Miss Ellie, J.R., Bobby, and Ray! It would have been a massive mistake to recast the character of Jock Ewing with anyone. What Clayton did do is become the new husband of Miss Ellie and he did a better job at it than anyone could have expected.. I also like Clayton because he has a quiet kind of strength and that was illustrated in the storyline where JR tried to make him throw Sue Ellen off The Southern Cross but Clayton refused even though he had to lay off hundreds of workers. Ultimately he saved his refinery by making a good business deal with Ellie. Clayton managed to get out of dire situations without ever lowering his principles.