Favorite stage 4 boss in the series?

Quality: Satori because her fight is way more diverse than Patchouli's.
Fun: Aya, since her fight is fast-paced and keeps you trucking.
Music: Probably Patchy or Murasa. Both really fit the fight.
Character: Marisa.
Overall: Ayayaya

If it's about the character,it' Seiga.If it's about the music,Seiga again,if it's about the actual boss fight,it's Satori,cause she has a total of 20 spell cards and as you know will use differently depending of your shot type (Which is confusing, but awesome) . And her nonspellcard is one of those nonspells that i know what to do at it,but still bomb.Overall if i think about a Definitive Stage 4 Boss Example in Touhou,Satori will be the 1st to come to my mind.I also like benben cause she takes easier on you than the other stage 4 bosses

Oooh this is a toughie. I would say probably Aya. I enjoy the feel of the fight, its not that hard even if topless wind god can get cruel sometimes. She pretty much single-handedly elevate MoF into something fun and is a good example of the kind of pacing and difficutly the entire game should have had. On Hard mode at least.

Stage 4 bosses are usually either "the boring late game boss" or the "different depending on stuff" boss. They're not bad usually but they just feel like they couldve' been so much more. Take for example Sega Master Bimbo, she has some interesting ideas with the Yoshika familiar but because its TD, it just turns into something mostly trivial and the only reason survival players are even remotely scared of her is because her 2nd non can be a butt sometimes (although even that can apparently be avoided reliably with a BORINGASS strategy) - 'she fight isn't rubbish but it could be much better. It could live up to the Lunatic name of the difficulty for example. Murasa also has this "i'm boring but still kinda hard" feel to her which is always an interesting one. My thoughts are... why not just SKIP the first three attacks she has and start out with the 3rd non, then vortex then ghost harbor. Keep it brief but fucking relevant instead of padding it out?!

No, Aya understands this. Aya's nons are actually different from each other and not just 3 attacks with the other two having less bullets than the last one. So Aya wins in that regard.

Then there's the category of bosses that change and I would imagine a lot of people would vote for them simply because having the option to face different bosses is more content and gamers today praise more content regardless of the quality of it so why not?! Seriously though, Patchouli and Satori are very cool bosses both but they just never seemed to hit the same level of "this is perfect" as Aya sorta did. As a person who has strong preferences for shottypes I just can't help but think that well... Satori with ReimuA is Murasa syndrome and Patchouli with ReimuB is really not all that exciting. Sure these bosses both have more interesting alternatives waiting on the other shots but that doesn't do jack shit for me if I don't want to use those shots.

Sisters type bosses? Well, again it has this feeling of "the other options might as well not be there" for me. That's why it would be better for me if ZUN did something similar to what, i think Relick suggested, and had the Stage 4 boss you face depend on something you choose. Maybe by being as simple as a FinalA/FinalB kinda choice while having the bosses being worth roughly the same amount of score so as to actually have a choice.

Wow, this is really hard. But I'll pick Aya just because 1. I like her. 2. The music goes with the danmaku SO WELL. 3. I like the music too.

As a character, Satori is my favorite stage 4 boss Satori is just so cute. And hella smug. I love that. But as a fight, it's the Prismrivers. Very intense with cool patterns and grazes. The penultimate on easy/normal is probably one of my favorite grazes in the series so far. For music, it's Aya. I like her theme. I think that sums it up. Prismrivers is the best stage 4 boss, Satori the best stage 4 grill and Aya has the best song.

Satori. Grazing her first spell feels so good. The character-specific cards are also really fun. MariB's fight is my favourite.