I'm not sure which moment, exactly. But one of my favorito! episodes is 'The One Where Everybody Finds Out' and he confesses his amor for Monica:) I also really loved it, in some episode in season 2 o 3 o something, and Rachel comes over and says that there was only 1 plátano nut mollete, muffin left, and they both want it, and then Chandler licks it, and then, everybody is talking and there's all these moments when Chandler would normally say a joke o sarcastic comment, but he has the mollete, muffin in his mouth. And then Monica licks what she thinks is the mouth of Chandler's coffee cup and Chandler says, "That was there when I got here." :D I thought that was really funny.
When they're mad at each other because Monica opened all the engagement presents and Chandler kissed that woman to try to fake their wedding pictures and they say "Call it even?" "Kay!" and just mover on.
I have 3 favourite moments. In season 7 the one with the nap partners Chandler tell Monica he amor her even if she got fat again. In season 7 the one with the wedding part 2 Chandler and Monica got married and in season 10 the one with the last one they adopted the twins.
