Whatever you can get your hands on, test them all out if you can. I myself have spent years using different programs. but you wanna limit yourself to afew first. For starters the most popular are fruity loops, reason, garageband (mac) and acid.
I started with reason and have stuck with it. although I've used tons of programs in the past, I'm really looking into getting Logic Pro. Watching those online training videos about their Sound Sculpture synth just makes me drool, I hear tons of pro dnb artists use logic, and their sound engine is just amazing. Anyway, those are just my thoughts. Hope this helps any!