Boy, this one is really tough... I would say...
Favourite character, Girahim, maybe? Maybe I just like his theme... otherwise, I guess skyward sword Impa (for spoiler reasons) or Tetra... augh, Tetra is really cool...
Least favourite character... hmmm... There is something about the windmill man I don't like, but I can't quite put my finger on what... I don't really hate him enough to call him "my least favourite character" ... IDK...
Also, I would like to give a special mention to Navi, I think she's really cute and I think people don't hate her as much as they actually hate just having the game hold their hand.
Favorite character: Linebeck, hands down. Though Marin comes in a close second.
Least favorite character: Zhant. I just found him to be poorly done in multiple ways. He was a filler character until Ganon's reveal and served no real purpose.
Zhant really got me until they revealed him as a deranged, wimpy minion of Ganon, I mean, I don't even mind Ganon being the true final boss, but I really liked hime more whne he was the creepy powerful vilian, I would've liked him more if they kept that image all the way through... Ganon himself I didn't mind cus I really liked the fight, even though some people don't like it at all.