My two favorites are not sex sounds and are too soft that you probably would miss them in a video, but are love grunts, nonetheless.
I worship the little barely there grunt(really just a gust of air) Justin makes right before Brian says I love you the second time in 510. Oh My Freaking God!!! I can't even stand it!
And I melt everytime at the little whisper of a grunt Brian makes after the kiss after Justin says that "yes, yes I will marry you, I will marry you." GUH GUH GUH
These are both so soft they are almost inaudible, but I turn my audio up to max every time cause they both just make me want to die!