Hmm, this is a tough choice. I usually tend to stay away from most incest doujins. However, I do know that sometimes the term "Onii-chan" can be used as a term of endearment for a slightly older, unrelated, male character that the female character grew up with, like in this one for example
Distance - Peach Temptation (spent 15 damn minutes finding it). I guess what makes both of these options so tempting is that it involves you being in a position of power/trust.
As for the master option, its bit of a hit or miss category for me. Some of them are pretty good like Mai Favorite while others are... ugh. It just makes you wanna reach in there and punch the guy's lights out.
So I guess I'll vote master.