What metric are we using? The developer whose games I like the most? The developer who treats their employees best? Or treats their customers best?
Valve has produced mostly bangers, seems to treat customers well and is by all accounts a great place to work. They've also been pushing development for gaming on Linux. Hard not to go with them, even though it's debatable whether they could be classified as a game developer anymore. But that's fine.
Remedy deserves a shout-out for sticking to their guns, and continuing to produce weird artistic games that push the envelope in the AAA space.
I'm not as high on BG3 as most people (though it's obviously a great game), but Larian also belongs in the discussion surely. I only ever hear good things about them.
Finally, the developer who inspires me the most is probably Lucas Pope. I love his ability to think outside the box and find entertaining gameplay loops in seemingly mundane things, but moreover I am just so impressed by how multitalented he is. I still can't believe Obra Dinn was a one-man production. I love his artstyle and the music he makes as much as the games themselves.