Several months ago I tried a lot of different software and ended up using Clip Studio Paint. Reasons:
- it was pretty cheap (only $50 one time with free upgrades to new versions)
- it wasn't slow on my laptop, unlike Photoshop and Krita
- it is designed mainly for manga / comic creators but can also be used to do 'painterly' things
As far as free software goes, there is FireAlpaca and Krita. FireAlpaca is what I started with, it is simple and doesn't have as many features as others, but it's fast and somewhat geared towards comic / manga artists. Krita was too slow to be usable on my machine, but otherwise was so spectacularly good I was a little heartbroken that I couldn't use it.
Really a lot of it comes down to what interface you like best; they are all different. As far as I'm aware, all of the paid programs let you do a free trial, so I would just try out a bunch.