A Link to the Past takes it for me as long as we can include mods like the randomizer. The games in its original form, Super Mario world and Chrono Trigger might take it.
For its time Secret of Mana was the best but it has not aged as well as Zelda or Chrono Trigger. Mario Kart is probably the master of not-aged-well games on SNES.
Fan-favorites Super Metroid and Yoshi's Island was never my cup of tea. But the atmosphere of Super Metroid and the art style of Yoshi's Island is still some of the best ever.
Mario all stars was probably the best value in a single cartridge. But since the best game in the collection, Super Mario Bros 3 actually plays better on NES the improved graphics is not enough to make the collection top SNES ridiculously good library. For both Mario Bros 1 and 2 I however prefer the All Stars version. The Lost Levels one can skip.
Two more games that I really enjoy and revisit is Mickeys Magical Quest and Turtles in Time. Turtles in time is one of the best arcade-style action games ever and the music is a great companion when running. Mickeys Magical Quest have awesome boss and enemy designs based Pete. Both are fairly short games one can finish in about 2 hours.
edit:
Oh and the lack of RPG games is probably mostly due to them never releasing on the system in the PAL-region. The ones I have played was done years later on other systems or emulator and sadly I do not feel that many of them hold up well. Apart from Chrono Trigger that simply is great in all aspects relevant to the genre.
