If you're into simple JRPGs with role-casting fun (both playable and NPCs) and very Japanese-styled gags, then go for it. Still, it all comes down to your wallet.
The 3DS version is the original version, while the Switch version is the same game with QoL updates, the horse, Outings, and most importantly, the Makeup & Wigs feature that allows one to unleash further creativity in creating their own Mii characters. The 3DS version is great for automatic role-casting and easy Mii search thanks to SpotPass and internet access to search Mii characters costing nothing. The Switch version requires Nintendo Switch Online subscription to use other players' Mii characters and sharing the Mii characters yourself.