I use both every time I edit a photo. I open my images in the software that came with my old camera, paste it into Photoshop to resize it and finally paste it into paint shop pro to edit it. Sometimes I edit it in Photoshop but only if I want something that specifically can't be done in paint shop pro. I'm used to where everything is in paint shop pro and through laziness can't be bothered to learn about Photoshop at the moment. I'm slowing doing more and more in Photoshop. Neither can do exactly the same job as the other. So really and truly, I'm lucky to have both.
My view on it? Paint shop pro is great for quick editing and the odd touch up. Photoshop is more for heavy use, if you know what you want in the first place and know how to do it.