From a player perspective,
Zelda is harder due to:
--Larger world with set of objectives which must be completed in some order. IE: You need the bow, before you get the lance, before you get the ice wand. A program could endlessly wander in the wrong temple for centuries before it decided it exhausted the whole area. (Not to mention the hidden walls&#x2F;areas).
++Mario levels are completed in a mostly linear fashion (ignoring the short cuts).<p>--Limited resources. Bombs, arrows, etc.
++Mario can always jump&#x2F;squish, and fireballs are infinite.<p>--Game changes as items are acquired. A block may be liftable in phase3 of the game, but not in phase1&#x2F;2. An area may drown you in phase1-4, but may be swimmable in phase5.
++Mario death is always death.<p>My number one reminder why Zelda would be harder is that temple where most of the walls&#x2F;floors are bombable and drop you back to the bottom (except one). A computer learning without manual training of some sort would be very interesting to watch.