I started out using MS Paint and I used that for a long time. I experimented with a couple other programs like paint.net, Muro, art rage, and ect. When I finally got my art tablet and drew in SAI for the first time in a while I hated it but my best friend liked it and encouraged me to continue so I did. I started to really like SAI and now it's my main program.
I use krita! Totally free and totally awesome!! I can get some pretty good stuff out there, and if I need any REALLY good filters (or if I need to make a gif out of a drawing) i use gimp. They both do more than I could ever hope when it comes to drawing!
I use FireAlpaca for inking and then I use Photoshop to do the rest. Long time ago I used to use SAI, but it was so difficult for me I had to give it up Besides, Photoshop fulfills some of my interests Paint Tool SAI couldn't.