After so many years, I still have to say that Adobe Photoshop is the king in this realm. As for Photoshop 7.0, which I currently own, I would say I'm completely satisfied and I really appreciate its well-roundness in terms of features and functions. It's true there are many substitutes available on the market, and it's fair to say that there's no point to use photoshop when all you want to do is adjust a photo's contrast. But if you ever involve yourself in some sort of designing or creative art producing task, you will find photoshop just makes your life so much easier. Its excellent integrability makes it the only thing you need to turn your brilliant idea into real work. It's fairly complicated and it does require some time and effort to get to handle it. But in my opinion Photoshop definitely worth the effort. My suggestion is spend some time learning it and try to master it, then you can get more and more from the software, and the skill might prove to be really useful at some point.
San Francisco, CA