This is one of those questions that's always tough to answer. And the answers will always change.
For me, I think the best game ever might be Chrono Trigger. It was a pretty short RPG from Square Enix before Squaresoft bought out Enix. It's a SNES game that you can buy in disc and digital formats these days.
But that was back in the day. Now, Square wouldn't know quality if it hit them square in the face with a bat.