Whoops fail, make that... aseprite. I am used to using Photoshop, so this isn't too much of a stretch or too simplistic... Gotta have layers!
I know some others that rely on the game maker sprite editor too... but isn't it just a basic editor with animation support right?
I prefer Graphics Gale to Asesprite but only for a few reasons. ..It does have some problems though. Nothing too bad, really.
Gimp yeah! I know it's an unpopular choice, but I've been using it for a year, so... I just understand and know it know, and I won't likely change. It is pretty good, just a bit complicated, so once you get it, it's all good.