I used to use pirated PS as a teenager, and switched to Gimp later on. My experience has consistently been: for basic selection masking, color changes, and minor adjustments(i.e. things you would typically do to photos), they're equivalents. For graphic design, Gimp lacks in certain features that add flexibility; the text tool is not as robust, and there isn't a direct equivalent to effects layers. The UI of Gimp tends to have more "irritating adjustment" involved and forces more early commitment. And PS has a much deeper set of content creation options - especially so in the later versions, which I've read about but haven't used.

I'm interested in learning Krita next. Krita is more explicitly an creation app but it also bleeds into other spaces in its new versions as it accumulates more features. It's gained animation tools, and its interface more closely resembles the classic PS look. Krita has a lot of velocity which makes me think it may surpass Gimp as an all-rounder in time.