I use (mostly) Photoshop, but it’s more out of habit than any real technical advantage (outside not needing to spend time acclimating to a new set of tools). From what I’ve read, GIMP now supports animation, though I haven’t used it. From time to time I use Anime Studio Pro and Blender which are both pretty powerful.
That said, try not to let yourself be limited by any particular program choice. At their heart, GIFs are moving pictures, which can be as varied as any art form I can think of. I appreciate a rough hand-drawn animation as much as I do a technically flawless exhibition of the capabilities of 3D software on a loop.
Make weird stuff and have fun. :)
btw, gimp and blender are both free, so get downloading (and do the tutorials, ffs). <3<3<3