Manga Studio 5/Clip Studio Paint is absolutely fantastic if you have a lineart style. I haven't explored its painting options much just because that's not really in my comfort zone right now, but I have seen some really beautiful paint-style works come out of it.
What I love about it is that you can save so much time coloring lineart with the smart fill tool. It's always been much more responsive than Photoshop and doesn't leave that awkward white aura around things that you fill in. The stabilization correction for lineart is really great too, and the brush options are great. Plus, I think it's been the easiest art program to learn so far. There are a lot of really great, really easy-to-follow guides on youtube that can teach you the essentials of the program pretty quickly. Best part: The software goes on sale all the time. You can get this program for like $25 about 4 times per year, around the usual sale times: Black Friday, Christmas, some time in the spring, and usually a summer sale.