I like GIMP, I've been using it since I stopped being able to get photoshop on the pirate bay (idk, like 2008 or so), so I'm pretty used to it. I've heard good things about Krita, but haven't dove into it, may be better if you're starting fresh.
I find GIMP quite versatile, from making animated gifs, original clip-art-esque compositions and (a ton of) political compasses. A bit of a learning curve when you get into advanced features, but I think comparable to about 2008 photoshop for basic image manipulation tasks.
Just a few examples from my memes folder