That's a good but tough question to answer.
Photoshop is great, but for me a pain to use because it's too much stuff packed all in one. It does have brush settings to play around with, but I found it a bit messy.
Other options are;
Paint Tool Sai - simple and easy to use, it does what it does. It focuses mainly on drawing on one singular piece at a time.
Clip Studio Paint - This program is what i'm currently using. It's more flexible, it can work on animations, books, comics, and just plain illustrations. You can easily create brushes in here .You can get a 30 day free trial, or wear an eyepatch.
Krita - completely free. It's actually pretty decent. Fast to open, fast to use. Perfectly viable, especially if you just wanna get something out there without too much worry, with a "Who cares, let's do this" attitude