what software is the best ?

You mean mixing?

I assume he means to ask what software is most capable at creating beats and synth tracks, or something along those lines. It really depends on your level of proficiency with audio software and your desire to learn. If you are a complete beginner, try working with GarageBand until you get the hang of it. Granted, GB is limited, but you should be able to use it to get your feet wet. Logic and ProTools are the most common audio suites. Both work excellently, and it really is a matter of preference for most people.

Ableton Live would be another program to look at if Garageband isn't enough for you.