Photoshop is the most popular photo editing software around. It is the industry standard today and is used by professionals and hobbyists alike. It is fully featured and allows for an extensive amount of photo editing jobs to be done.
Pro Industry standard
Photoshop is used by professionals everywhere in a wide variety of fields including photography, graphic design and digital art. It is the de facto standard for image manipulation. If you've seen a magazine ad featuring a model, you've probably seen the effects of Photoshop. You won't be alone when using Photoshop.
Pro Packs a staggering amount of functionality
Photoshop is the most fully featured image editing software available today allowing you to perform highly advanced image manipulation.
It has tools for RAW image adjustments, lens correction, retouching, image stitching, HDR, fixing framing. It supports most professional color modes and file formats. It includes extensive lists of filters, styles, effects, fonts as well as tools for painting, sketching and typography work. It understands both raster and vector graphics. It even includes tools for video editing, working with 3D objects and support for 3D printing.
Con Learning it can take some time
While you can relatively quickly learn how to perform a few basic image editing tasks, understanding Photoshop's ins and outs can be difficult. It's partially due to the sheer amount of functionality that Photoshop packs (and understanding that some of the advanced functionality can take a while to understand on its own), and partially due to it being aimed at professionals with little hand-holding for novice users.
Con Asset management capabilities are lacking
In Photoshop asset management is done through a separate program called Bridge. As Bridge is supposed to be a file management tool for not just Photoshop's files, but for files generated by all of Adobe's applications it covers a breadth of capabilities, but not depth.