This is probably the first question one have in mind when starting in digital art. There are other options like SAI, for example, but I'll focus on that two of the heading.
I started using Photoshop more than ten years ago, not for drawing but designing. I was working for myself and some projects as a graphic designer (making banners, web designs, photo editing, signatures...). At that moment I was drawing in paper, but when the first Wacom tablet reached to my hands I questioned myself which software I'd use.
Despite of having experience with Photoshop, I decided to start drawing digitally with Corel Painter, probably 'cause I had the thought that Photoshop was better for "editing" or making other types of works, and Corel Painter was the best choice for just drawing, not else.
Couldn't be more wrong.
Missing some photoshop tools when I was working with Painter, I recently decide to give Photoshop a chance. And I'm really happy with it. I love Painter and the way you can manage your brushes, it has an incredible potencial, but I also love some ways I can work with Photoshop and which I can take advantage. I'm actually working in some drawings with Photoshop and thinking about using this tool as primary, cause it's really surprising me.
As is usual in this "world", everything depends on you and the way you love to work. And couldn't be a greater reason for experimenting and trying all the options you have near you. Don't be like me, don't think just one option is the best because of prejudices or whatever. Test all the softwares as much as you can and probably one of them will make you work easier or just more comfortable.
In my case, despite of my love for Painter, I've found in Photoshop a really powerful tool for drawing and I'm gonna give it a great chance!
Listening to: Paradise City - Guns n' Roses
Watching: Breaking Bad
Playing: Mario Kart 8