I'd have to say Aeralfos from TP. It has always been my favorite in the series. I find him very cute. I don't know why though. And he is the miniboss in the Sky temple, which is my favorite of al the temples in TP.
I would miss a couple Darknut, Iron Knuckel, and most of all chu-chus. Iron Knuckles and Darknuts are the ones I have had the hardest time with but they were the easiest to beat at times. Oh and the chu chus are my favorite enemies because I have the most fun fighting and were the easiest to beat through out all the games.
I would say................................ Stalfos or Iron Knuckle. Iron Knuckle knows how to fight hardcore. Stalfos, knows too, but not too much, I guess.