ProMotion and Ex Gen are completely different programs, but you probably need both.
Ex Gen would be a good option for animated textures, explosions for instance. But ProMotion is actually a pixel art and sprite package, so would be nice for making GUI's and icons and stuff like that.
The middle ground would be to go for a traditional art package, like PSP9, in fact I'd take PSP9 over any other art package, because it can cope with everything from sprite and pixel work to particles and object textures. I prefer it to Photoshop, and it's much cheaper. So I would suggest getting a demo if you can, and trying out all these programs, and decide among them which ones you need, if not them all. I would suggest Ex Gen and PSP9 as good options, because PSP9 is better than ProMotion for everything, but Ex Gen offers something more unique, that you can't easily make yourself in an art package.