People will hate me for this but I think that the wind waker was a little overused
I know the game was named after it but still. Most of the time you used it everytime you sailed anywhere even twice In a lot of cases
I did like the goddess harp because it was simple and easy to use rather than forgetting the song checking what it was and then playing it.
The ocarina is nice that you can make up your own songs, and the spirit flute is cool, a bit frustrating for me at times though. But I'll have to be different and say wolf howl. I love wolves and the howling songs sound so awesome.
Out of all the games I played, the Ocarina of Time is the most useful. Arguably the Wind Waker could be more useful, but I don't count it as an instrument.