ableton for sure... is simple to use and is super flexible... the thing it has over the other things like reason etc. is that it's a pretty standard style of program so and as you get deeper into music, everything that you can do in anything else you can do in Ableton. if you get used to reason or fruity etc. and you really start getting into music, you'll find that you quickly have to move on to bigger and better programs and learn an entirely different interface which would be like starting again anyway. plus, it's quite easy to switch from ableton to cubase/logic/sonar if you need to in the future.

machina