Clip Studio Paint is amaaaazing and I use it for all of my work. It not only comes with fantastic built-in screentones, but as @El_Psy_Congroo pointed out, it also automatically calculates color into screentone. It's an amazing program and I can't recommend it enough.
It is worthwhile to point out though, as @conbon100101 mentioned: screentones are not just the property of manga; plenty of other comic creators have used them, and even superhero comics have used them, quite frequently actually. In western comics, for quite some time they were known as "ben-day" or "ben-day dots". They're famously employed by Roy Lichtenstein at greatly-magnified proportions for dramatic effect, but they've been used in western comics as long as there have been comics.
I'd also recommend Clip Studio Paint for the ease in making brushes, especially pattern brushes. I've made more than a few that have cut my production time in fractions.
Regardless, I say go with screentone to cut down production time, regardless. Clip Studio Paint has superb built-in screentones that will make your production much, much smoother and easier, but in general screentone is just a fantastic option. I like color, but not as much as I like screentone; there's just something about it that I feel is superior to color. There's something about greyscale in general that I think asks and invites the reader to meet the creator halfway and interpret the colors, which is a good thing. It involves them in the process of creation, and that makes the comic connect more profoundly. At least, that's my take on it!
Hope this helps, and I hope you find something good for you. The best thing is to determine what you feel suits your needs. It may not be exactly your wants, but as long as you satisfy your needs and requirements, the rest provides a little wiggle room.
