Marisa: she's the first character that I ever wanted to be my friend. First off, witches rule. Second, the Master Spark is the best attack in anything ever, it's a huge laser beam!! Third, Ze! (ok I know it's not really a catchphrase. Even Uzume says ze. But I associate it with Marisa) I also like any song that's supposed to be sung by Marisa (IOSYS etc., my favorite song is NO REPLY).
IF: is the coolest character on this site! The design is great and I like all of the different roles she gets, from being treasure hunter to being the Planeptune intelligence. She's also an edgelord/chuuni my favorite character archetype. But at the same time she's the straight man of the three. And dual claws are a great weapon!
Uzume: is thick-headed but she's actually strong, so the other characters just have to go along with her. I also like the idea that she's a symbol for dreaming of a better world and protesting for it. Also like that she uses Ore as pronoun.
Greatest:
Neptune: everything about Neptune is great. I love her upbeat personality and weird way of talking. I love her interest in Games, and her positivity about everything related to them. I love the sci-fi design. I love her catchphrase (Nepu!!). Also her original portrait is just omega kawaii. If there's someone I want to play Sonic with, it's her.
Dejiko: even just the basic idea of Dejiko is great, she's supposed to be the store mascot that gets more customers into the store, but then she behaves the total opposite of that. She's lazy, rude to the customers, fights with Rabi-en-rose and fires the Eye Beam at customers. Also then there's her backstory like of being an alien princess which is cool.
Random:
Compa: she is a character which is very empathetic to all other characters, which I really relate to. Also there are so many small facts and details that make her interesting, and all the lines that she says that you just wouldn't expect from her.
Mokou: I really like her design, the suspenders and pants are unusual on an anime character. Her song is my favorite in the Touhou OSTs. She's also the first EX stage boss that I ever beat. If it's Mokou vs Kaguya, it's obvious for me which side I'm on.
Alice: she's a bit of a weirdo and that makes her interesting. I'm fascinated by characters who are antisocial or struggle with being social. Alice to me falls into that category: wouldn't it make sense that she makes her dolls not just for fighting or housework but for talking to her if she's lonely?
Cirno: other characters call her an idiot and treat her like she's not really strong, but Cirno doesn't care. She just carries on and does her thing!