Pencil and pen are the best. I tend to use both. I use pencil to sketch out the picture, then draw the outline over the pencils marks. After rubbing out the pencil, I can either colour it straight away, or scan it and colour it by computer. Drawing takes an awful lot of skill and practice. The mouse is fiddly, though it is possible to do decent art with it, but it can damge your eyes looking at the screen all the time drawing your picture.
Paints? Those are left to professionals with art qualifications...