I've moved this thread to Program and Utility Discussion. Please be sure to post your threads in the correct forum next time. Thank you.
It really depends a lot on what you're doing. If you're used to GIMP, switching to Photoshop may not actually be the best move. There are a lot of things that other programs do much better and for everything else GIMP does equally as well.
Pyxel Edit is really quite wonderful, I've got it running right now. It's pixel art only though, so if you're wanting to do other style graphics it isn't going to work for you. Photoshop does not do what Pyxel Edit does at all. Pyxel Edit is optimized for making tilesets, so everything about it is set up to optimize doing just that, like being able to map with the tiles and draw on the map and have the tiles update in real time. If making pixel tiles is something you want to do, even casually, it's worth every penny and more.
If you want to do tiles more like Ace's or MV's RTP, Krita might be a good move. It's not as awesome for making tiles as Pyxel Edit is, but it does have something that is impossible to find in any other painting program, a wrap canvas feature. Okay technically it does exist in Painter too, but the one in Painter is terrible to the point of being useless. Krita's got some crashing problems and it isn't good for editing things, but for making things from scratch it's really great and beats photoshop in a few things, like brushes and tablet support. Plus it's free.