I'd say PS4 for now. The PS4 has open world Action RPGs (if you like that, personally I hate them, the stories are always lackluster and the worlds are boring to explore) JRPGs (turned based and Action RPG), fighting games, some platforming games, simulation games (with things like Stardew Valley), beat em up games, shooters, and a ton of other stuff. The Switch still doesn't have too many games. But the Switch will be getting Pokémon (presumably Gen 8), more Zelda and Mario games, and a lot of first party stuff in the future. I know there's a some 3rd party stuff out too, like Sonic Mania, Sonic Forces is coming, and there are some RPGs IIRC. If you're willing to wait on those to come out and you like those games then get a Switch. If not you can always wait a year or two until there's a decent library.
It's really about what kind of games you want. I have a PS4 for some bigger titles (and now JRPGs are coming to the system), a Vita for JRPGs, visual novel type games, ports of older games (plus whatever I can buy cheap), and a 3DS for the first party games and some of the third party RPGs, beat em ups, and whatever else is on the system because it has a little bit of everything.
So just get whatever has or will get the games you want.