So, is this a thinly-veiled "wich 2hu wud u fuk" thread?
...All right, all right, I'll take it seriously. Ya'll no fun at all :V
Nailing this down is pretty much impossible for me. Besides a tiny amount, I like pretty much all the 2hus. If you wanted me to make a Top 5, I'd STILL have tons of trouble because there's so many I could put there. But let me try. Note that this is NOT in order in the slightest, I hate doing that and I can never nail down an order anyway:
-Momiji: My waifu 2 laifu. Momiji is simply the cutest little wolf on the planet. I'd fallen in love the moment I saw her. Her lovely white hair, her red eyes...love~ But besides her cute and sexy looks, I like her personality as well; she feels like one of the more grounded and sane residents of Gensokyo.
-Byakuren: Byakuren is an interesting character in my eyes. She's got the fact that she's trying to help Youkai but at the same time preaches something that goes against their base nature. She has a strong sense of conviction, but an adorable and moe ditziness in how she fails to watch her subordinates and friends closely. Her theme is one of the most amazing in the entire series, and she interacts with a lot of other characters I love like Shou, Nue, and the like. Plus, her rivalry with Miko makes for good stories. She's also beautiful: that long, luscious, gradient hair, her womanly stature, and her lovely dress are all just amazing. Plus, you know: those bountiful Buddhist boobs. Sorry, I'm a simple man to please.
-Reisen: Well, first of all, she's a cute gun-toting bunnygirl. But besides that, Reisen is, at least to me, one of the few Only Sane Women in the entire series, so I love portraying her as a person who is just plain DONE with Gensokyo's wacky bullshit (you can see this in Inebriated Fairy Erotica). I absolutely despise most canon depictions of Reisen, as Eirin/Tewi/The Whole Fucking World's chew toy and as a useless bunny. She's way better than that, and I will fight for Reisen's dignity till I collapse. She's one of worst treated characters by the fandom, which makes my love for her only stronger.
-Miko: When TD came out, I gave zero shits about it. I pretty much left the fandom. Well, now I'm back, and I love the ever-living fuck out of Miko. Why? Because she's SWAG AS FUCK. No other way to put it. Miko has such a self-confident, overblown-yet-awesome sense of "I am fucking amazing and I love it". From her cape, her bold personality, to the crazy shit she pulled in her backstory, Miko just plain don't give a damn about what you think. There's no character like her in Touhou. Even Remilia is still a bratty kid, and Yukari is too lazy to do anything. Miko has the power AND the confidence. Her theme in TD was...okay, but really anticlimatic, however the HM remix was simply amazing. In terms of design, she's pretty good, I kinda wish she had...something else to her. She's so confident but she's not even that womanly. Byakuren has her clearly beat when it comes to projecting maturity, if you know what I mean. Then again, no one can agree on her boob size--I like her a little big, but not Byakuren-level.
-Tenshi: Like Reisen, Tenshi is another character who is treated awfully by the fandom--or did all the masochist jokes stop? Regardless, I love viewing her as a lovably-bratty girl who just wants to have some fun, and she's gonna get her fun by any goddamn means possible. She strikes me as the kind of person who would go out and start shit, and as a writer I love those kinds of proactive characters. I like her cocky and self-confident, not whiny and masochistic like so many others do. Plus, she's beautiful: all that long AND blue hair (Seriously, her hair is SO GODDAMN PRETTY HOLY SHIT) is good enough, but that dress is just lovely to look at. ZUN's character design is near-flawless. She also has the slightly unfair disadvantage that I ship her with an OC.
Wow, that's five. Uh...there's so many characters that I'd love to put here, so you know what? Let's make this ten, because honestly Touhou has a stupid-huge cast anyway:
-Marisa: Main character represent! Marisa is so much cuter than that other MC, Reimu, with her blond hair and cute witch outfit. But besides that, I love Marisa's no-nonsense-let's-just-barrel-into-things-at-full-speed attitude. Marisa does what she wants, and she doesn't care if anyone else has complaints. Reimu is always bitching about her job and wondering when she can get home, but Marisa? Marisa doesn't even have to solve incidents, that's Reimu's job, but she be all like "Yeah, I'm gonna go solve this by myself, Reimu, 'cause I just can". I love how, in a world filled with stupid-powerful youkai and gods and demons and angels and all sorts of crazy stuff, Marisa is just a simple ordinary Magician who nonetheless can go toe-to-toe with nearly the entire cast. Marisa is just badass. It's as simple as that. Oh, and her themes are always godlike, 'cause she's awesome like that.
-Sanae: Green Reimu Shrine Maiden represent! I didn't actually care a ton for Sanae for a long while, but in the past few weeks I'm starting to really like her. Like most of the girls I already mentioned, Sanae is really assertive and confident. I just like those kinds of girls. She's a connection to the outside world, and she's got that adorable "YOUKAI HUNTING FUCK YEAH" attitude. Plus, she's really pretty...I like long-haired girls, in case you haven't guessed.
-Sakuya: Alright, I guess it's time to go mainstream. But truthfully, the reason for Sakuya's popularity is pretty easy to see. Now, while most people see "knife-throwing maid" and already have their thumbs up, I like Sakuya for her character archetype: the mysterious maid or butler to the Big Bad who is very powerful, making you wonder just why they chose to work under someone. It's always fun speculating on these characters, and they just are fun to use. Sakuya's no-nonsense personality also helps here. She's the kind of character who'd kick someone's ass and then whip out some tea to calmly sip over their opponent's lifeless body. You can't hate someone like that. Also Flowering Night is amazing, especially the SWR mix.
-Shou: Well, here's an uncommon choice. Poor Shou. No one gives the slightest two shits about her. Well, I do care about this tiger. She serves as a great foil to Byakuren, and has the same kind of adorable ditziness to her, except Shou can actually see when shit isn't working unlike Byakuren who is just stubborn. Of course, Byakuren usually fails to heed her advice. The only common portrayals of her are "Nazrin's Master" and "That Dumb Chick Who Loses Stuff All The Time", both of which I feel do a great disservice to her. Sure, Shou's ditzy, but she's still cool. She's a goddamn tiger. A sexy tiger at that...
-Aya: FINAL CHARACTER TIME. Even after 9 goddamn characters this was still really hard, but Aya surpassed everyone else because, surprise surprise: she's another "I do what I want", takes-no-nonsense characters. I just love them, I'm sorry! Like Reisen and Tenshi, I hate Aya's common depictions, as a panty-shooting pervert or as some intrusive shithead. That ain't my Aya. Aya's a journalist who loves to snoop out stories and shady stuff. She goes where she wants, and gets the scoop no matter what. Sure, she exaggerates her articles, but I'd attribute that to her fun-loving personality (though, to be honest, the few snippets we get don't even seem that much worse than Akyu's articles). Aya's never stopped: she's always on the move, which makes for great interactions with the rest of the cast. Plus, she even has TWO foils: Momiji for the serious foil, and Hatate for the ditzy foil. She's also got a more mature feel to her than the most of the cast--not as mature as, say, Byakuren, Eirin, Yukari, etc., but she still feels like a young adult where the rest of the cast are teenagers (Reimu, Marisa, Tenshi, Youmu, etc.) or kids (Cirno, Mystia, Wriggle, etc.)
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Yes, I am well aware that you probably didn't intend for people to pick TEN characters, but blame ZUN for making such an amazing and vibrant cast. There are STILL characters who I feel had a shot at this list but had to sadly be cut, like Remilia, Ran, Seija, Suika...these are a pretty good representation of the characters I REALLY like. As may seem obvious, I like characters who are independent: they go out and DO stuff, instead of just sitting around.