How well do you play and who will be going in with you?
Are you very serious about the game, your wizard has the best gear, you win a lot of fights solo if needed and pick up boss cheats fast? Easy to Medium.
Are you like me and just play for the fun of it all, don't always stack your deck right, hate to do the math to figure out what stats will give you the most bang for your buck and can never quite toe the line on boss cheats? Hard.