While Photoshop is pretty damn neat sometimes, I don't think it is geometrically better than any other graphics program. It's geometrically more "full" than other programs, but as far as interface and simplicity go, it's only arithmetically better than the others.
Thus, the choices. If you use every filter every week and try every setting, then you are probably a professional photo-manipulator. You need Photoshop. For every other user, price and familiarity will be the main factors. Even MsPaint can make you a "Save your drama for your llama" banner.