Both were pretty darn good, but I found MM to be harder than OoT (I don't know why...)
Also, I liked the ending to OoT a LOT better than MM! I mean, at the end of OoT, you fight a huge monstrosity of your worst nightmares, with a thunderstorm going off as you square off in a confined area. It's almost something out of a good movie.
In MM, you go to a weird area with only five little kids and a huge tree, and they all ask you to play with them in exchange for your masks. Ermm.....I kinda found that to be odd. More like something that Hitchcock would come up with. Besides, what did all of the kids stand for? Were they symbols of SkullKid's terrible youth, or what? At least the fight with the actual Majora's Mask was plenty challenging, and interesting, to say the least.
Overall, OoT just beats out MM in my book, even though I got the collector's cartridge for MM
