Last time I used gimp was like 6 years ago so take my opinion with a grain of salt but I do feel Photopea is easier to use.

I have no idea which one is more powerful but for the average lowly user like myself Photopea has had all I need and then some. It’s also a browser only application which for me is a boon but I can see some people preferring a download instead. I would recommend going on the site and messing around a bit to get a feel, it’s free to use.