Koei Tecmo. It's not even close. They've been with Switch since day one and nearly all their published titles since it's release has a Switch version day one with the other versions. I'm also convinced they're the reason Persona 5 Strikers came to the Switch.
Was about to call out the entire thread for not mentioning Koei Tecmo more.
They even supported the Switch with titles older than the Switch, despite questionable financial viability.