I'm surprised people dislike Tamani so much. Although, I can't say I'm not bias on this one because goblins are one of my favorite races. She could certainly use more depth though, or possibly a way to disable her if the PC has a penis but doesn't actually want to fuck her senseless.
Regardless, my least favorite character solely from a design standpoint is easily Venus. I don't necessarily dislike her character, but I always found it annoying that if the player chooses to have sex with her on a regular basis it will quickly result in a bad end. There isn't any forewarning about the event either; Venus never indicates she has any insidious plans that would indicate the player should exercise any caution. I'm aware that talking to Venus more often will prevent this from happening, but the presence of the bad end is still strange and annoying. As a result I tend to avoid interacting with her altogether, but then she becomes a nuisance when I'm trying to search for Whisker Fruit or Equinium at the Lake. At least you can disable her encounter if you choose "Insult" when you first meet her.
My least favorite character in general is probably Kiha. Her stereotypical tsundere personality has always been rather cringe-worthy to me; and it's irritating having her descend on my corrupt characters shouting about how she'll "NEVER BE DEFEATED" after I've already stomped her ass a hundred times. I always wished there was an option to force her to leave you alone at the swamp without having to pay her off (as if she is a legitimate threat) or take her in as a follower. An option to scare her off or perhaps take her in as some kind of slave would had been nice.
I can't really say for sure which character is my favorite. Although, for sake of completion I'll say Katherine. I love the amount of depth the character has and enjoyed actually being able to help her out, take her on dates, give her items, etc. She is probably the most detailed lover in the game, and I really appreciate that. My only issue with her if I'm remembering correctly is the game pretty much assumes the character wants to bang her. If you help her out twice it automatically results in the player and Kath going on a date and then fucking which I did not initially see coming. But still it's a minor complaint.
