Ubisoft right now,

Is this for exclusive games or in general because I'd say Capcom as of recently. They did bring Mega Man 11 and the X collection along with the SF 30th Anniversary game and MH Generations Ultimate as well. And there's a number of other interesting games coming out later on too.

Epic Games from Fortnite.

I gave my vote to Namco Bandai, but was torn between them and koei. Ultiamtely NB has released Naruto trilogy, Dragon ball xenoverse 2, DBFighterz, Katamari Damacny soon, One Piece red , One piece pirate warriors 3, Dark souls remastered, Will be bringing Tales of Vesperia, Taiko, My Hero one justice, and a few other games. The thing with Koei is many of the games they've ported to Switch were not localized in despite the fact their PS4 counterpart had been translated. Example many of the Atelier games or Dragon Quest heroes. Granted DQ heroes may have been a SE issue, Koei was still involved I'm sure in some way.

I think Bethesda is working best with nintendo but it is only because of the graphic engine they use

talking about switch generation i would say ubisoft

Bamco, Bethesda, Square-Enix.

the name of the engine is "id tech6" for doom and wolfenstein 2 both are great titles and they are running/looking good on switch. theese are the best two 3rd partiy games on switch for me at the moment and skyrim is also from bethesda.

I'm not sure I'd vote for them, but I think Square Enix deserves some consideration. Between the Bravely series, Octopath, and the recent bringing over of FF games, it seems like a solid partnership building.