Aseprite is currently the best tool, but GraphicsGale was the OG and works fine.
I personally am unhinged and sprite directly onto a sheet with usenti, then import it elsewhere with specified tile sizes to preview.
This is probably why I’ve yet to finish an animation.
If you’re doing it via sprite sheet → import, then GIMP or just about any art program with a 1 pixel aliased brush and layers would work great. I’m not sure why I insist on not using layers even when digitally painting, but no one should follow in my footsteps.
Edit: another factor for not using aseprite is that the UX was intolerable for me without plugins/changing the cursor sheet/etc. And the way the UI doesn’t scale naturally but does some pixel integer scaling crap because it’s insistent on being pixel art is incredibly offputting. Also the preview doesn’t go to 1x magnification for some reason. onion skinning is overrated for pixel art at this scale anyway smh. ← coping