I wrote this as a response to someone who complained that their digitally inked pictures looked too much like a coloring book. Then I realized, maybe it could help other people who have the same issue. This is a comparison of various digital art programs, when you're just concerned about INKING.
I've been doing digital inking for years. I find that different programs behave VERY differently for inking and create very different feel to your work. Every few years I find a new favorite program.
I can't stand inking in Photoshop, because you can't flip the canvas and the line smoothing feature doesn't really do anything. It's like working on paper with a ballpoint pen, and the paper is taped in position.
Inking in Manga Studio is awesome for technical drawings and backgrounds, thanks to its rulers and guides, and you can get nice smooth strokes- but if you want smooth strokes in one part of the piece and then rough, textured strokes in another part (like most furry bodies are usually rendered) you're our of luck. I switched away from using this program because it SUCKS for color and final rendering for posting on the internet; it was designed for printed work.
SAI makes super clean, smooth, bold lines, which are great for easy coloring and a cartoony look, but bad if you want a soft & organic feel. Results often look like a coloring book.
SketchBook Pro will give you a very soft & organic look because you can't make a completely smooth and opaque brush, and line smoothing is either nothing at all or extremely wide curves, and the thickness of strokes doesn't vary much... I've found that inking in SketchBook Pro takes about three times as long as with other programs, because I have to go back and correct a lot of spots, and manually widen others by adding extra strokes over the original line. Line-work done in this program is a pain in the butt to color, but the results can be gorgeous. I only finished a few pictures with this before deciding it slowed me down too much.
The best I've found for me, so far, is Clip Studio Paint. It's similar to SAI in smoothness and line weight variety, but it handles small, quick, textured lines a lot better. Results can look like a coloring book at times, but Clip Studio also combines all the features I used in Manga Studio and Photoshop. Switching to this program meant I could complete a comic in one program instead of switching back and forth between four! It's also a bargain price, you can buy the program for less than the monthly cost of "renting" Photoshop.