It is my opinion that a steel string acoustic is far more versitile than a classical guitar. You can play just about anything on a regular acoustic guitar where as the classical, nylon string guitar seems to be limited. The nylon strings have a softer mellow sound that doesn't translate well.
I also think the transistion from a steel string acoustic to either electric or clasical would be easier than going from classical to electric or acoustic.
Hope that helps. Good luck