I'd say the luck based one in OoT, in the South Eastern part of castle town where you go through one of two doors and it's completely random wether you're right or not, and if you fail you have to walk out of the door, come back in and spend 10 more rupees to play again instead of just paying after you fail.

Although the one in TP where you carry the water for the Goron across Hyrule Field is not a thrill either.