I have used Graphic Converter, Photoshop and GIMP for years, and GraphicConverter always winds up being the program of choice for image editing (perfecting a photo, stitching together montages, changing file type, adjusting file size and quality to fit the need). Like any good OS X program, a novice can start getting results quickly, but LemkeSoft has also built in a huge number of features that present users with increasingly powerful image manipulation and editing as you use and learn the program. The program is self explanatory with good help files and responsive support, but if you have used image manipulation and processing software in the past, then GraphicConverter will seem easy. Additionally, the program has been continually improved over the many years I have used it, with frequent substantive updates and responsiveness to taking user requests and turning them into new features.
This program is a winner if you are looking to process photos, do complex image manipulation, change file formats or combine images. I would have continued using GraphicConverter even if it were considerably more expensive, and I highly recommend this program for anyone who cares about images.