At first it was awesome because she was the first one, then I played the others and released she wasnt that great. Although Barinade comes a close second.
My favourite was Phantom Ganon purely for the creepy and original picture elements...it was good to have a boss battle with a slightly sombre fear atmosphere. Reading the comments in this thread I seem to be alone in this thought.
I find that Phantom Ganon was the toughest too. Not that it was actually challenging...just that in his second phase since he's constantly moving around and changing the spacing between you two, it can sometimes take a while to score a hit.
Beaten: All but SS
Completely beaten: TLoZ, TAoL, ALttP, LA, OoT, MM, FSA, TMC
Up next: OoX