At this point, it's between Navi, Tatl and Zelda (ST). Everyone else was just so much chaff.
Navi wasn't all that helpful to me, but to a newcomer she was pretty good for a navigator.
Tatl seriously did nothing at all, she constantly berates you for asking her for help (she assumes the player is an OoT veteran, which I am), but she always wants you to reunite her with her brother despite forcing you into the situation in the first place.
Zelda (ST) was what I wanted – a playable combat ally. Although I wish she could've done more (like, playable by a second character or something), she still served her purpose well. I still had my fair share of problems with her though.
So I'd say my favorite Zelda partner is NaviTatlZelda.