On the face of it this is a dumb question, I'll admit that, Mario and Zelda are both extremely different experiences that work on extremely different levels. But when you think about it preferring one over the other sort of defines what kind of gaming experience you prefer.
I'll try and explain exactly what I mean by that.
Mario, to me, has always felt like the epitome of video game systems firing on all cylinders. It's a very pure gaming experience. The mechanics are wound tight, everything feels good and balanced. The word I'm trying to avoid using here is 'fun'. Mario games are always fun, moment to moment, always. There's a concentrated joy that comes from all Mario games, like skulling cordial straight from the bottle.
Zelda, on the other hand, is the closest thing Nintendo has to the video game as experience, as a story told through mechanics. Zelda, unlike Mario, feels like an adventure. It's a game that you might take a little more seriously.
So in that sense I've always thought that preferring Mario or Zelda goes a long way to defining what kind of gamer you are, as corny as that sounds.
So with that: which do you prefer?