Definitely go madness spec Assassin then. You'll have enough DPS from lightsaber and force powers separately to kill most weak, standard, and some strong enemies, but you WILL have to use both for elite and higher level enemies.
Overall, there isn't a single class in the game with access to both that has enough power in either lightsaber or force powers to kill every enemy in the game without using the other alongside it. If that's what you're looking for, you are out of luck.
No that is actually exactly what I want basically, to combine the 2 in equal measure to take down my enemies. I wouldn't expect to take down elites using only one side. =)
Ok then I will try madness.