They were all great characters.
Michelangelo: My favourite when I was very young just because he was the "party dude" but sometimes he was a bit too dumb.
Leonardo: Underrated. The burden of leadership is a heavy one. I remember reading some comic story or something where he left the Turtles because they didn't appreciate him and they thought they'd be fine without him, but they all got captured by Shredder or something and he had to rescue them. Let that be a lesson to you.
Donatello: "Does machines" is not adequate to describe the smartest Turtle. Without him we never would have had the turtles travelling through time. The thinking man's choise.
Raphael: The cynic, a lot like me in many ways. Certainly the turtle with the most depth in the movies and for this reason my vote goes to him.