Naughty Dog: They've always been my favorite studio. Jak, Uncharted, and The Last of Us, are all some of my favorite titles. I feel a little disappointed that their games are getting further apart in release date, but I think they still make some of the best games.
Santa Monica Studios: God of War (2018) solidified them in the S tier for me. I thought God of War 1 - 3 were good games, but God of War was genuinely a best game ever contender for me.
Insomniac Games: These guys are beasts. Between Ratchet and Spiderman, they have a lot of good talent.
Media Molecule: I'm a bit let down by Dreams, but LittleBigPlanet was a favorite during the PS3 era. And I'm hopeful that they will return to making their own games, instead of simply a game engine.
Team Asobi: Astro VR quickly became one of my favorite platformers ever. I don't tend to like platformers, but I thought Astrobot: Rescue Mission was genuinely amazing.
Sucker Punch Productions
Polyphony Digital: Racing games aren't my forte, but I think they do a good job.
Housemarque: They make great games, but they're only getting started in the AAA space.
Bend Studios: Days Gone is pretty much the only real game they've made in almost 10 years.
San Diego Studios: Modnation Racers was a game I really loved during the PS3 era, but they've largely become an MLB studio, which is pretty disappointing, as I have no interest in that.
London Studios: even though I love VR, they haven't made anything to really capture my attention. They've got so many eyetoy and Sing Star games that it's hard to even be excited by them. Blood & Truth is a good step in the right direction, but they've got a long way to go.
Pixelopus: They're a tiny studio.
Support Tier (I really don't think these ones should count among the main studios. Nixxes does great technical work, but they're still getting passed over because they don't make anything for themselves.)