it's hard to get a SHORT list of my favourite pairings in touhou.
at first place an exequo with yukari x reimu and kaguya x mokou, totally fell in love for them
then.i love so much mari x ali, since the first doujin i have ever read was about them
after this i'm pretty fine reading sakuya x meilng, aya x momiji, eirin x reisen, sakuya x marisa, koishi x satori and, sanae x reimu, sanae x kogasa and so on.
i'd like to see some characters not so developed in the most of doujinshi, like flandre, she is my favourite character and i could just die for a flandre x remilia doujinshi pretty decent, but even flandre x marisa could be good. also yuuka, the ultimate sadistic, is an interesting character, paired with anyone tsundere or passive characters could be pleasant but she seems to not be so loved in the circles.