Mostly first-party. Even before I got a PS4 Pro last year, that was still the case. Since I got the PS4, the only third-party game I bought on Switch was Undertale. I probably won't get more than a small handful of third-party games on Switch at this point, unless they're Switch exclusives. Provided Octopath Traveler doesn't go to PS4, I would purchase it on Switch.
Lifetime Sales Predictions
Switch: 144 million (was 73, then 96, then 113 million, then 125 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima