I'm afraid I'm about to make a "me too" post here...

Define your aims (and read past threads).

In brief, music splits firstly 2 ways - audio programs with things like mp3 and .wav and secondly, various ways to make a computer play and write music. The second group can be further divided into programs that aim mostly to give things to listen to or music to read.

Within the second group, my own favorites are Cakewalk (versions of which can also mix audio thought I've never tried that) for sequencing and the use of abc (and because of my own limitations, I do often use Noteworthy as a helping step on this) for notation, or at least for the notation I want to try to help produce.