my rankings of the c sides by difficulty

[The Sun]

8- Old Site. This one was very easy for me and I beat it in less than 100 deaths. Kind of a joke.
7- Golden Ridge. I expected this one to be really awful with the utilization of wind and arrow blocks, but it wasn't so bad. I actually had a lot of fun, especially on the last room!
6- Reflection. I saw a yt video of somebody beating this before playing it, and I expected it to be really hard. However, it actually was pretty easy and straightforward. I'm glad that they put a checkpoint before the bumper blocks, because that was the most difficult part for me.
5- Core. This one was pretty anticlimactic after the Summit, but I kind of liked the more chill vibes from this one. I especially liked the throwback to previous chapter's mechanics in the final room.
4- Forsaken City. It's absurd to me that the first c-side was so difficult, especially when followed by the easiest one. This one was rough, and took 2 sittings to complete. I especially had trouble with the last room, but that's a common theme with c-sides.
3- Celestial Resort. I sort of have a love-hate relationship with Chapter 3 in general. The timing is absolutely the focus of this level, and that's probably why I placed it so high. The first room gives me World's Hardest Game vibes.
2- Mirror Temple. This chapter is interesting. The first room requires pixel-perfect jumps and pushes your patience to the limit. The second room is incredibly straightforward and most people can complete it without dying. The third room is absolutely brutal with the usage of dash blocks and red bubbles. I'll be honest, I did not enjoy 5c very much.
1- The Summit. This shouldn't surprise anybody who has played 7c. The first 2 rooms are pretty unremarkable, with the usage of vertical wind and super-walljumps. The third room is probably one of the most difficult screens in all of Celeste, and took me around 3 hours to complete. However, I absolutely loved (nearly) every second of it, as I died and learned from my mistakes. The ending leaves you with a feeling of huge accomplishment. This is not only the most difficult c-side, but the best as well.

[ChekinNooget]

i thought 7c was pretty easy imo

on the other hand, 8c was horrible

[Ryouski]

My ranking from hardest to easiest by death count was…

1. Summit (700)
2. Resort (354)
3. Core (343)
4. Temple (227)
5. City (150)
6. Reflection (100)
7. Old site (83)
8. Gold Ridge (68)

[dudeover]

Here is my:
1. Summit 581
I thought it was impossible but after +-10 times when i got to double dashes part, I did it. Took me 2 hours but it was a little bit fun somehow. The last room's experience is a definition of Celeste. You're progressing with every death and you don't want to give if you ever start this side.
2. Core 325
I hate 8A and 8B but this was actually fun. I rebeat the first room to prapare for the final strech. Even when I died right before the heart, I wasn't frustrated and beat this side after 3 atts.
3. Mirror temple 203
Without these wall jumps I wouln't beat 7C so... ok (I still died right before the heart of course).
4. Celestial resort 191
It wasn't that hard for me as for the many other players. Maybe it's beacuse I watched guide about jumping on Oshiro's head. But I would done it even without a guide cause it's only the two jumps at the end that are hard, the rest is free.
5. Reflection 159
It could be soooo painful but that checkpoint saves the side. But I still HATE FEATHER. I'm playing on keyboard and that thing is still impossible for me.
6. Golden ridge 128
Somehow I fluked a few last jumps but it was still hard for me even tho I like wind gimmick.
7. Forsaken city 98
There's not much to say about it. It's just fine.
8. Old site gd-side 34
Fun cosmo blocks hehe

I thought I'll never beat C-sides. They look terrible at the first glance. But after few easy ones, the rest seems more doable. Soooo I think I can beat Farewell (maybe).

[ShoneChello]

here's my list based on death count (G means that I got a golden strawberry):

1. The Summit ─ 584
   
2. Mirror Temple ─ 508
   
3. Core ─ 253
   
4. Reflection ─ 415 (G)
   
5. Celestial Resort ─ 321 (G)
   
6. Forsaken City ─ 171 (G)
   
7. Golden Ridge ─ 150 (G)
   
8. Old Site ─ 110 (G)

Technically not a C side but the skull is yellow so... Farewell ─ 2254

By the way, It's possible to die after grabbing the crystal heart. If that happens, you will have to try again.