I've played and enjoyed both, but if you can only get one I would recommend 4. It's a classic, honestly, and I've heard the Switch version of 5 has some performance issues; not sure if those ever got patched. The farming and crafting are like Stardew on steroids, and there's skills for literally everything that can improve your stats in various ways. The characters can get a little anime trope-y but if you don't mind that I'm sure you'll end up with a few favorites! Personally I always loved Dylas, Arthur, and Vishnal from 4.
I've played and enjoyed both, but if you can only get one I would recommend 4. It's a classic, honestly, and I've heard the Switch version of 5 has some performance issues; not sure if those ever got patched. The farming and crafting are like Stardew on steroids, and there's skills for literally everything that can improve your stats in various ways. The characters can get a little anime trope-y but if you don't mind that I'm sure you'll end up with a few favorites! Personally I always loved Dylas, Arthur, and Vishnal from 4.