for me it depends on my mood if i am in a pissed off mood or if i'm mad at my Master then i need to top but if i'm in a good mood i prefer to sub to him.
the reason that if i'm not in a good mood i top is because if i'm subing to my Master and i tell him to Foff or something like that i get punished for it but if i'm toping i can let out all my anger and not have to worry about getting punished for it