i think vegitto because we all know vegitto was way lebih powerful than ssj3 and he never fight seriously he kept toying with buu till last time so we do not know his full potential.so i think vegitto.
THOUGH SSJ4 IS THE POINT OF SAIYAN POWER VEGETO IS FAR STRONGER SINCE goku WAS NO MATCH FOR SUPER JANEMBA BUT GOGETA BEAT HIM EASILY AND VEGETO IS STRONGER THAN GOGETA SO VEGETO SSJ2 IS THE STRONGEST