my favorite ocarina song is the song of healing. i could just leave that song on for hours and fall asleep to it. a close second to that song would be Zelda's lullaby. and my third fav. would be Requim of Spirit or Song of storms, i still can't decide XD
For Ocarina of Time, my favourite playable song is the Minuet of Forest, followed closely by the Requiem of Spirit. The Minuet of Forest is really calming song and sounds playful, like Saria's Song. I like to play it from time to time just to hear it.
The Requiem of Spirit has that sense of finality. This is the last time Sheik will teach us a melody. This is the last dungeon / temple you have to trudge through to waken its respective sage. No matter how many times I play Ocarina of Time, being taught the Requiem of Spirit makes me feel just as accomplished as I did nearly 10 years ago, when I learnt it for the first time.
In the case of Majora's Mask, I didn't find the playable songs to be as memorable as I did Ocarina of Time. However, I'd say my favourite playable song is Oath to Order. The scene when you first learn it is incredibly well done - and the music itself creates this feeling of "now, we get serious."