I can't choose between the original game and Crisis Core. The original is the one that started it all. It had an excellent story, wonderful characters and the materia system was amazing! Crisis Core was amazing in the fact that even though you only had one character, Zack was presented to be one hell of a main character. I have no love for the DMW, but it was an interesting concept and I'm always up for new ideas in the games I play.
But if I had to, I would go ahead and say the original was best. Just because it started it all.