I've used all three products and I prefer Gimp. My wife prefers Krita. It's great to have choices.

Never heard of krita, I’ll have to check it out.

GIMP is honestly a lot better than it used to be, especially with the g'mic plugin, which is insanely powerful.

For Photoshop users, there's also photogimp, which makes gimp have a Photoshop layout and keyboard shortcuts.

Though personally I use krita most of the time, which has g'mic built in nowadays.