Fun: Shooting gallery in any game, even though I tend to suck at them...I really dont have a favorite "official" minigame. I make up my own. In ST I just ride the train around and shoot signs, in SS...I throw pumpkins all over Skyloft, in the water, at people, I hit people with the beetle, I put bombs by people. My brother tortures remlits. In TP I run around castle town in wolf form and watch the people scream and run. Oh but I guess the bug catching game in SS is kinda fun.
Frustrating: The roller coaster of pain in SS, aka the minecarts. It requires a lot of memorization. I can share a tip though: put beacons on the gaps so you know when to get ready to jump. The only thing this minigame has given me that's not a headache is a few one liners.
(When you fall off) "I'm Link and welcome to Jack@$$."
(Before you get on) "Welcome to the roller coaster of pain! Here's your barf bag, here's your diaper. You'll need them..."