They have different (but overalapping) use cases. Gimp is more for photo editing and krita for painting. But if you’re looking for a photoshop alternative, gimp is probably the way to go

Krita seems like a better run project and more competently designed thing, but like the other reply they’re kinda made for different things

Krita is specific to digital painting/illustration. Gimp aims to be more of a drop in replacement for Photoshop with both photo editing tools and painting workflows