okay so chiateto is a lot to deepdive into i will be honest so this reply will take a while to be answered

if you want to only stick to the surface and Not really dig deep into their stories and them as characters , i like chtt because of the whole annoying senior x tsundere junior trope sue me . chtt and mdch are the same in that way but the big difference is how tetora looks up to all of his seniors and how hes so over the top hyper around them especially kuro (es1) , but chiaki is So Annoying that not eventually tetora can put up with him and finds him annoying as well . another difference is while midori just finds chiakis constant affections Annoying to deal with and embarrassing , tetora takes them as being treated like a kid/not like a man and gets far more frustrated with them .. but! in es2 in a very recent interaction (fooor..? christmas?)! he learns to accept them! and he even hugs chiaki first! but back in es1 hed get all Aghhhh taichooouuu dont hug meee>_<! its not manly! but secretly he Would enjoy it even a little even if he didnt wanna accept it

But! if we dig into stories! there are PLENTY! one of my favourites has gotta be hero show for both of their characters .. but mainly for yaoi . so in hero show chiaki is making them LARP superheroes and finally tetora has enough of it so he storms out to cry in the rain but he runs into kanata who tells him a buncha stuff he doesnt understand a word of , and how him and chiaki are similar , and finally how chiaki actually went out to look for him in the rain and then got sick like passed out or somethin so then tetora goes to the nurse room thing and it leads to one of my Favourite interactions ever

T: Don't force yourself to talk! You'll seriously die, Taichou, you dumbass!
C: Ugh...... How pathetic, what kind of "ally of justice" is defeated by the likes of a common cold!?
C: My own helplessness is resentful, horrifying! Move, body of mine! Wasn't it a mere three straight all-nighters t most!?
C: ...... Shit, I did everything I could do but it seems I'm at my limit. It's regretful but I must leave the rest to you! My comrades! "Ryuseitai"!
C: Bring back love and peace to this world! Battle with evil as much as I did!
C: Protect everyone's smiles...... u-urk!?
T: Taichou~! It's no good if you die~!

but moving onto more recent stories , supervillain is By Far one of the most important stories for them as characters and them as a duo . i wont summarise the story because everyone already knows it so ill point out some of my favourite bits

C: (Ahh.. that's right. That's exactly what it was.)
C: (That was all I ever wanted to do.)
T: And that's why I respect you, Morisawa-senpai. I admire you, and I love you. I have no actual capabilities and I'm terrible at producing results through my effort, so I can't be you no matter how hard I try.

okay i lied thats the only bit you get right now because i am Busy! with packing up some stuff but! i will be more than happy to provide more once i have some more time

But! overall i love chtt i love them i love them i love them so much theyre So special to me