Obviously, Photoshop is the most popular and used premium choice, but Paintshop is a more affordable alternative. I mean, you're talking about a huge difference. In fact, Photoshop demands annual fees of around $119 a year! Anyway, though, you do get what you pay for. The bottom line is the Photoshop simply has more tools.
I have never really enjoyed Photoshop much and never really gotten used to it to the point where it is easy, as I have with some others. I do not doubt that it might be better than some, but at this point I would just rather stick to what I am used to.
I will go for Gimp because it is 100% free and many professionals actually used it from Art works, Image manipulation to graphics for 2d videogames. It is a visual art software that requires zero dollars. It is a very flexible software you can use for both hobbies and graphic design jobs.
Paintshop is more or less a clone of photoshop. Everything you can do in photoshop is possible with paintshop. But things such as controls and settings are easier to understand with the photoshop. And that's another reason why many people make use of the photoshop. I'd say it'd be not unreasonable to say that paintshop is lagging in market due to popularity factor as well. Atleast that's what I have noticed.