Can be for the American Super Nintendo or the Japanese Super Famicom. In my opinion, Chrono Trigger is the best. I have beat it for the first time recently, and enjoyed the 20+ hours I spent on it. 20 hours well spent.
Chrono Trigger and FF6/3 are definitely at the top of my list, so good that square enix sees no need to update the graphics (though that'd be awesome) my other two favorites are; Secret of Evermore, and Earthbound.
Edit: whoops, definitely add Mario RPG too. Geno's theme song is now playing in my head.