What's your favorite Cas moment? I know it's hard to pick, but I'm curious xD For me, it was when Cas told Dean how to stop Lilith while saying he absolutely can't help him. His first time of defying Heaven, but he went on with it so calmly. I basically love whenever Cas cleverly turns the table and be sneaky bastard while he's cornered, but this moment made me fall in love with his character.
Oh my dear anon! I saw this in my emails first, and all I glimpsed was 'what's you favourite Cas moment?' And then I just went to open tumblr to read the rest here, because I knew I wanted to reply ASAP. As I was opening the window I was pondering, and the moment that INSTANTLY came to mind was Cas in The Monster at the End of this Book exploiting a loophole in the angelic 'can't stop a prophecy' stance and LO AND BEHOLD this is what you are describing!
I too did not LOVE love Cas until that moment.
In fact, before that moment I strongly suspected that while he had been shown to sympathise with Dean, that ultimately his loyalties would be with Heaven and that he would forever stick to his orders and Dean and Sam would probably have to stand against him and maybe even kill him by the end of the season. I still, I suppose, in simplistic terms, figured he was a villain and/or antagonist until THAT MOMENT.
So, yes, I guess it IS my favourite Cas moment :)
It's when Cas came into his own and when his rebellious nature first truly showed itself. But it also showed the inner STRUGGLE that continues to inform his character - because while Cas WANTED to help Dean and clearly was EMOTIONALLY connected to Sam and Dean's plight, he couldn't shake off his ties to Heaven. He was stuck in an awkward in-between - not completely with Sam and Dean, not fully throwing himself in with humanity, because he still believed that Heaven/angels were or could be good/right, and not whole-heartedly a part of Heaven either, because he also believed Heaven was treating Sam and Dean and humanity badly.
And I guess that struggle, of Cas having a foot in both worlds, having understanding and sympathy and love for two groups that typically do not mix, and as a consequence being unable to find belonging in either, is one of the core things that draw me to him (albeit subconsciously for the most part!)
BUUUUUT there are SO MANY OTHER MOMENTS I enjoy just as much.
I just ADORE the 'sorry scene' in Reading is Fundamental (as horribly painful as it is) - Cas so guilty and regretful/remorseful and trying to communicate that to Dean (as well as trying to distance himself from his feelings and what he's done because it's too hard to face), but not coming across as sincere, at least not enough for Dean, who in any case is not listening properly, understandably considering how hurt he still is over what Cas is trying to apologise for, and Cas asking Dean to 'go first' with the Sorry! game, because Dean is not blameless, and - ugh, it's such a messy tangle I like that scene a lot okay!
I love Cas with Dean in the Green Room at the end of S04, trying so hard to keep to his faith that Heaven's course of action is just, but so clearly affected by Dean's arguments that bit by bit find their way inside him and break apart Heaven's brainwashing - that was GORGEOUS to watch! Literally seeing Cas fight the philosophy Heaven had conditioned in him and find the courage to rebel :)
ALL OF CAS in On The Head of a Pin (partly for the same reasons as above - oh oh his PAINED EXPRESSION when Anna explains what he's feeling is doubt, and of course probably he KNEW that, but he'd been lying to himself that it wasn't, that he was still a loyal warrior of Heaven/God, only then FALLEN Anna apparently recognises part of herself in him and it's confirmation of his worst fears so he denies and denies until he no longer can!)
Cas trying to kill anti-Christ Jesse is also a really cool and intense moment.
The 'TALK TO ME' scene in Hunteri Heroici where Cas admits his guilt over what he did to Heaven while high on Purgatory souls has left him suicidal.
The crypt scene in Goodbye Stranger.
Oh oh, Cas so desperate to save Samandriel in Torn and Frayed.
ALL OF CAS in Heaven Can't Wait (but esp. when he has to leave the crime scene full of blood and is shown head bowed over the Impala - so vulnerable and AFRAID).
Really... almost every time he was onscreen during S09 :) I was GIDDY over him having his own onscreen arc for the first time that season, so much of it will forever retain a sense of fondness for me because of that.
I think, basically, my favourite Cas moment is CAS :p