Not OP, but my opinion:

Affinity Designer is a very good vector editing app. Switched to it from Inkscape due to performance and UI issues. To me, it's more convenient to use than vector things in Pixelmator Pro.

For photo editing, I don't like Affinity Photo. It seems powerful, but too much for me to learn, so I use Pixelmator Pro for simple photo editing (although I can never remember where the tool I need is). Maybe it's better for pros, though.

For quick pixel editing/cropping I use Acorn — it's fast and the UI is not overloaded.

+1 for Acorn, my image editing need are pretty light and Acorn does everything I need.

Both are great. I prefer Pixelmator's polished macOS UX, but Affinity is more feature complete.

-- hobbyist experience

Affinity is closer to a Photoshop clone.

I've been using Pixelmator Pro a little recently, and I turn to it now for its AI features. Cutting a subject out of its background? It makes the "Magnetic lasso" feel like MS Paintbrush. I had to design a heavily 'shopped Christmas card recently, and those features cut down my work by a lot.

I own both Affinity Photo and Pixelmator Pro. I find the UI using Pixelmator to be more user friendly. This could be because I come from many years of using Photoshop and I found the way Affinity deals with layers and effects to be counterintuitive to me.

That being said, both products are solid and likely a matter of personal preference or specific feature needs.