Ahhhh, Fruity Loops... Good times.

I think Pro Tools is as "Pro" as you can get. I've heard many great productions from FL and Reason just the same. It's not so much the program as the producer making the music. So it is up to him/her to find his/her suitable program in which they feel most boundless in creativity. Haven't had/heard any productions made with Audacity (not that I know of, anyway) so I can't judge it. I'd try them all out to see which one works best for you. Some are easier to work with but might not provide the same functions as the other. My 2 cents.