As someone who has used a bunch of different image editing tools to make stuff (mainly for games, though i'm not an artist - i just need to make art :-P), Krita is fine. It has a bunch of weirdnesses (e.g. 2983942 commands to paste an image and all of them are kinda weird or missing in some way) and doesn't have as much features as GIMP but overall it is fine. Then again i found GIMP fine for a long time.

Though my favorite UX (and features) of all time is Paint Shop Pro 7 which i find superior to Krita (i have it installed alongside Krita, GIMP and Kolourpaint -used for minor edits since it starts instantly- on my Linux setup via Wine). I used it since Win3.x days in the 90s until PSP8 was released and they screwed up the UI. I moved to GIMP some time later when i started using Linux and used that for years. Some years ago i found a boxed copy of PSP7 anniversary edition, reinstalled it and despite not using it for more than a decade i found it much easier than GIMP and i'm using that since, until i wanted to make a plugin to assist me with texture painting for 3D models. Making plugins for PSP7 was very cumbersome so i thought to try Krita instead (Krita has an MDI mode which i like when working with images) and ended up sticking with it since making the plugin was relatively easy[0].

I'll download Krita's source code and try to build it and add the features i miss from PSP7 at some point, KDE people do not seem very allergic to having options so i might be able to recreate the stuff and behavior i miss from PSP7 in Krita.

In order of preference:

1. PSP7

2. Krita

3. Pixelmator (only under macOS of course and i only used an old version before App Store with the only alternative being GIMP running under XQuartz - i think GIMP got a native version later but i never used it)

4. GIMP (i found older versions easier to use, but every time they introduce a new major UI change i find it more awkward than before and now they're switching away from Gtk2 to Gtk3 -which i dislike the feel of- i decided to stick with Krita)

5?. Photoshop, maybe (i only used it a little in the past, always found it more cumbersome than GIMP or PSP, but it'll do if nothing else is available)

[0] http://runtimeterror.com/tools/kritaview3d/

That Time I Recreated Photoshop in C++