It's a pretty tough question! I like different songs in different ways, so here are 3 vocal songs I really like!
Yellow Zebra - Hyouketsu Musume. This is the song that made me a fan of Yellow Zebra. I like it so much, because Cirno is my favorite character, and, well, I really like the song. I found it near the start of my Touhou journey, and it might have enticed me to explore even more circles, or maybe more niche circles in particular? I found it through Osu. Come to think of it, Chirumiru helped in making Cirno my favorite character. I became more fond of her because I liked the silly baka in the animation. I still didn't know how Touhou "worked" back then, at least not much, and I didn't know much about the characters, too. But the "wonder" probably helped in something. I can't really articulate my guesses.
Shibayan Records - Fall In The Dark. It's just such a bop!
5150 - beat awake true heart. This too, is a bop. I listened to this a lot (and other songs by the same uploader) while I was painting a fence, which I considered to be sorta like a job/internship without pay. It was annoying or boring, much of the time, but it was also good from time to time, and I gained valuable experience.