I jumped the ship from using GraphicsGale/Photoshop as my main pixeling programs to using ProMotion [almost] exclusively. It is a very different feel from other graphic programs so it definitely is something you have to want to learn how to use, but it is well worth it, and I do a lot of pixel art animation.
You can make your onionskinning behave exactly how you want it to, whether you want to see a copy of every other frame within 10 frames in front of or behind the current frame you're working on, with half of the onion layers showing as transparent previews and the other half of them showing as specifically colored silhouettes... however you want to set it up.
The thing that took a lot of getting used to, for me, was that the layering is done differently than most programs approach layering. You create stacks of files. So the layer your background is on would be one file, whereas the foreground layers would each be their own files as well, and changes you make to them can be saved or discarded independently. (though I guess you could have each layer just be a frame of the current file, never thought of that... might have to play with that workflow and see how I like it
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So yeah, if you're serious about wanting a bitmap/pixel art tailored program, ProMotion is really a strong contender because you can do so much with it. But GrafX2 is really getting nice, especially for a free program that works on any platform. And it just added layering support semi-recently. I'm sure they'll add animation to the mix sooner or later.