I play 100% portable due to having an 11 month old daughter and wife at home if that makes any difference. A big thing to note is (for me) the experience portable is the exact same as it is on a big screen and for RPGs portable with headphones is the most enjoyment I've had from gaming in a long time.

1. Skyrim - I know it's been released 57 times already BUT playing it portable is something else entirely. I bought the game on release night for PC and played it on PS4 as well with the remaster. Since buying it on the Switch it's the only thing I want to do all day, I play it at work on lunch break and in bed every night. I brought it with me to the walk-in clinic last night and the dreaded hour+ wait time felt like minutes as I was just sitting there exploring Skyrim the entire time. It's one of the reasons I love my Switch so much, it brings full console grade games to a handheld (unlike the DS/Vita which were "lite" versions of games at best). 1.5 Super Mario Odyssey - (just... awesome, I have almost reached 100% moons and still LOVE playing it) If I wasn't so hooked on Skyrim this would be my #1.
2. Zelda BOTW - Fantastic game that does so much more than previous open world adventure RPGs. The movement system and ability to go anywhere is amazing.
3. Mario Kart 8 Deluxe - Even as a single player game this game is fantastic and it's the ultimate party game, everyone loves Mario Kart.