I would say that Devil's Trap and No Rest For The Wicked are the best in terms of the brothers being on the same page and working towards the same end IMO. Sam wasn't trying to atone for season long screwups; they were in sync to combat the season's issue ( save John from YED, save Dean from his deal ) and they ended on a cliffhanger that made us anxious to see what came next. The Man Who Knew Too Much was admittedly mostly Sam's hell trauma taking a front seat with the latter half being asshole Cas stuff but the brothers were united in stopping him. Season 7 would have been a great cliffhanger if not for the disappointing and rage inducing season 8 opener. With that being said all of the previous showrunners ( more or less ) before Dabb were able to craft a finale that showed the brothers working as a team. The exception being Swan Song which was insufferable and Alpha and Omega which gave us Mary which is just unforgivable.