I use Paint tool sai for both sketching, lineart and clouring.
I find it a really fun freely software, and you got the nessesary tools to create what you want, maybe something is easier with photoshop and illustrator, but all the tools you need to create something similar is in sai, it just needs some layer techniques and stuff to make the same outcome.
I use manga studio for my panel works, I find it easier for average exppresionism and panel construction, and generally nice to create whole mangas. I will still draw in Paint tool sai though.