There is no best in honesty. I do 95% of my work digital, and I have used a variety of software over the years. Photoshop is the industry standard, but if your just beginning there is no real need for it, and if your not going to work professional, there will probably no need for it either.
GIMP is free, I started with that.
All you need is a canvas and brush. That's it. Learn the fundamentals, don't worry about fancy software or filters and just draw. I got hung up on whats the best brush, and all that too back when I started. I was forced to learn with a hard round brush for everything in my school, along with the fundamentals and now even though I use Photoshop CC, I basically only use a handful of brushes and a canvas. 99.9 of features with the software is never used. Just get drawing and learning is the best thing you can do.
Failure, the greatest teacher there is!- Master Yoda
Thoughts,tips,insights and personal critiques over on my new blog at https://art-beat.blog/