Depends on your level.. Coral Paint Shop Pro for beginners and intermediate but Adobe Photoshop for a bit more advanced.
Depends what your wanting to do? Have a play with the on-line version of Photoshop - It's free and no need to install anything on your PC. https://www.photoshop.com/express/landing.html
Got Corel Paintshop Pro Photox2 - brilliant Especially if you are not an expert. Has instructions you can actually understand. Adobe - you need a degree in physics to understand. Try the 30-day free trial for both and see.
Get Serif Photo Plus X2 Its easier than Photoshop and far cheaper. There is also an easier version of Photo Shop 'Photo Shop Elements' again must cheaper. There are, however, some free programs out there I tried but lost the details, will check.
RE: Got Corel Paintshop Pro Photox2 - brilliant Photoshop is a fantastic piece of software, far superior to the rest. It may be a bit complicated but there are hundreds of tutorials on the net and a plethora of 'how to' books to choose from. Once you've got your eye in it's a doddle. Very expensive like.