Krita is great, and free.
Photoshop and CSP are the industry standard, though. I think it depends on what you've got, since you might want to stick to it for a while and "just draw".
gonna rehearse what others said and say krita is really good and CSP can do more if you bother with it i guess. i just use blender and krita simultaneously to figure out some of the trickier parts of drawing like perspective or how light is supposed to interact with very complex objects