I liked Navi....but I liked Tatl better, even if she was a meanie. Navi was nice and companion-like but i hated when she said useless info over and over again. Like when you're in front of a barred door she says something like 'you cant open this door with your bare hands!' Well DEEERRRRRR. it just made me angry like does nintendo think its players are that stupid so as to have navi repeat that crap over and over again?! But I dont care much, it wasnt that annoying. It was kind of expected that nintendo would put something like that in there, it makes sense.
I hadn't really gotten that far in OoT. Her advice was actually helpful, but that may only apply to first time players such as I.
However there was a time when I was playing the game, having trouble figuring out where to go, and she said "I wonder what Saria would think that we're saving the world." Later on, she repeats the exact same line twice. That was annoying.