The Supernatural fandom couldn’t get enough of the potential romance between Dean and Castiel for more than a decade, and the resulting interest led to the idea of Castiel and Sam also harboring hidden feelings for one another. Of course, it was the Destiel fans who got their happy ending, as the final episodes confirmed that Cas was in love with Dean - although it still wasn't quite what everyone wanted.
Despite this ending, there are enough reasons to ship either Destiel or Sasstiel due to both dynamics bringing points to each one’s benefit. Still, there are particular areas where Sam or Dean would have made Castiel happier if he had been with them, giving advantages to either shipping camps.
Destiel: There's More Passion Involved
Even in the times where Dean probably didn’t deserve Castiel’s friendship, there was a dynamic between the two that could be felt. They didn’t reach points where they would be apathetic to one another, instead, their clashes had a lot of heat behind them.
The times where the two had each other’s back saw the pair care more about their safety than probably necessary, always wondering how the other was holding up and being more upfront about how they felt if they disagreed purely out of their concern for each other.
Sasstiel: They Always Forgive One Another
Despite their great care for one another, the Winchesters and Castiel still did a number of bad things to one another. What was certain, though, was that Sam and Castiel would remain on good terms, no matter what the situation was.
Sam instantly forgave Castiel when the latter apologized for breaking the wall in his mind containing Lucifer, while Castiel overlooked Sam’s own attempts at his life when he became evil from harboring Purgatory souls. Sam never gave Castiel a hard time like Dean did, leading to the two developing a closer relationship over the years.
Destiel: They're The Ultimate Fan Couple
When the topic of fan fiction couples on Supernatural comes up, Dean and Castiel are the top choice for everyone. They embody what fangirls love to ship, with elements like romantic tension, genuine friendship, and subtle hints at something more available in this dynamic.
Not for nothing did Destiel take off in the first place, as Dean and Castiel carried these traits right from the beginning of their relationship to the very end. Their ups and downs were just the kinds of things that fan fiction enthusiasts enjoy.
Sasstiel: They Have Better Compatibility
Had they really become a couple, then Sam and Castiel would have been the perfect one. It comes down to the two always having their views aligned, with Sam and Castiel never disagreeing on anything and having a great relationship in general.
There wasn’t a conflict present between these two, which helped in keeping things between them on an even keel. To this end, a potential couple featuring these characters would have had a very long-lasting potential since they would be on the same page every time.
Destiel: There Are More "Moments" Between Them
There need to be certain charged moments that point toward a potential romance, and Castiel and Dean had this in buckets. More than a few occasions featured the pair in close proximity for no apparent reason, paving the way for instances where they had awkward interactions that resembled romantic tension.
The two also had big reunions and heart-to-heart moments, which, despite being infrequent, last in memory since these times had genuine sentiment behind them. Destiel fans have highlight reels dedicated to this very trait the pair exhibited.
Sasstiel: They Understand Each Other Better
Dean and Castiel might have had noteworthy emotional moments, but Sam and Castiel had much more in quantity. In fact, the later seasons showed Castiel approaching Sam for advice and for someone to talk to rather than Dean, as Sam didn’t make Castiel feel belittled or unimportant.
Castiel never turned down Sam’s ideas and plans, with the pair working together behind Dean’s back if necessary. Their approach was always to talk things about before making a decision, which is the most healthy way to be with someone.
Destiel: The Pair Are Shattered Without The Other Around
In the long list of heartbreaking Supernatural episodes, the ones that stand out are Dean or Castiel are mourning the loss of the other. They were inconsolable when either of them died or were trapped someplace else, something that is reminiscent of true lovers.
Dean usually had to drown his sorrows out by going through a depressive phase, while Castiel would throw himself into working out ways to get Dean back. Had Sam not been there, it’s more than likely that both of them would have been too far gone if their separation had been permanent.
Sasstiel: Their Embraces Have Reciprocity
It’s an important factor in Supernatural’s DNA for the hugs to be filled with love and emotion. While Dean was more than willing to embrace Sam, his hugs with Castiel were almost always one-sided due to Dean feeling awkward.
As for Sam and Castiel, their hugs became more and more intimate as the years went by, developing from their original hesitation to embrace. Sam never had an issue with this, instead initiating hugs later on as Castiel himself was more than willing to return his embrace.
Destiel: It's Canon
During his final scene on the show, Castiel seemed to confirm all the notions that Destiel was canonical. He confessed his love for Dean, which didn’t seem platonic in any way as Castiel expressed a true moment of happiness for finally being able to bare his heart.
Dean didn’t express his own feelings, although it was clear that Castiel had harbored genuine, even romantic love for him. But as Dean didn’t outright deny having similar sentiments, it is very much possible that he did feel the same way after processing what Castiel had said.
Sasstiel: They're Basically Jack's Parents
If Dean was out of the picture and Sam remained with Jack and Castiel, it would have turned them into an actual family. Castiel was more or less Jack’s true father while Sam was warm and comforting to him in a way that Jack would have felt the maternal component was fulfilled in his life.
Neither Sam nor Castiel wanted to see Jack get hurt, while Dean usually couldn’t care less about him and actively tried to kill Jack in Season 14. Jack could very well consider Sam and Castiel as his real parents, and the pair would have had enough reason to be together had they become romantic.