I seriously recommand Aseprite, this is the best sprite software I've used. It is 100% dedicated to sprite creation, so it handles animation, frames, layers, export with lines/columns, the pen tools are better than standard pen like in Gimp or Photoshop because they have a pixel-art option to draw pixel-art lines, with no adjacent pixels, etc.
It's just the best, by far. Try it, you'll see. It's harder to come back to another software.