Stage 1:
Favorite - Tossup between PCB and IN, but I'll go with IN. I really like Illusionary Night.
Least Favorite - I want to say EoSD, MoF, or UFO for being really bland, but holy hell, SA is such shit. When it comes to getting a 1cc in these games, I usually have the hardest time simply having a perfect run of Stage 1 and Stage 2, and that's even if they're easy. You know what happens when the first stage is actually crap? Shit doesn't hit the fan, but a truckload of shit hits a jet turbine.
Stage 2:
Favorite - These stages are also pretty bland, but their boss themes tend to be surprisingly good. With that in mind, this is actually a tough choice. I'm going to go with PCB since I like Chen's danmaku.
Least Favorite - MoF. Not much to look forward to here. The stage doesn't have much going for it (then again, none of the stages do), but Hina's battle is pretty boring. Plus, she has that crappy last card, but then again, Stage 2 bosses with at least one shitty attack isn't too much of a rarity
Stage 3:
Favorite - PCB. No contest. Alice is awesome. I don't know why, but IN's Stage 3 never interested me, and the same goes for Keine. EoSD's is fine, but it's nothing amazing. Both SA and MoF feel pretty much the same here.
Least Favorite - UFO. This doesn't need to be explained :3 (Even if ZUN fixes the stage, I doubt I'll be a fan of it.)
Stage 4:
Favorite - SA, SA, SA. Great music, great danmaku, Satori. Makes up greatly for the previous 3 stages in SA.
Least Favorite - I find all the Stage 4s to be quite fun, but if I had to pick a least favorite, it would probably be PCB's. I'm not too much a fan of the length of that stage, and the same goes for the Prismrivers. Patchy can be annoying, but her challenge is welcomed. MoF is also an aesthetically pleasing wonderment.
Stage 5:
Favorite - MoF. Very pleasant stage with a lot going for it. While it may not be as challenging as SA or PCB, it definitely has a lot of fun factor. Runner-up would probably be SA, with PCB following very closely.
Least Favorite - EoSD. The stage portion feels very uninspired, and while Sakuya is a badass, all of the Stage 5 bosses are badass to a certain degree. Runner-up would be IN.
Stage 6:
Favorite - Very, very, very tough. Just picking one, I'll go with MoF. Out of all the Stage 6s, I've easily seen MoF the most thanks to VoWG. I really enjoy Suwa Foughten Field and the sheer speed of Kanako's battle. Remilia and Utsuho both hold special places in my heart; the former for being a fun and consistently challenging opponent, and the latter for being extremely atmospheric.
Least Favorite - This is also a tough choice, mainly because I really don't care about Yuyuko, Eirin, and Kaguya. However, I'll just go with IN Stage 6A. Eirin really doesn't feel as epic as the rest.
Extra Stage:
Favorite - MoF. Extra is all about memorization and trick cards, and I don't think that anyone does it better than Suwako. MoF's stage is like a fireworks display.
Least Favorite - SA. I never really did like Koishi's stage, and the same goes for her cards. Penis danmaku has a special place in my heart, though.