I much prefer Teens over Milfs, however there's always a sliding scale when it comes to things such as this.
Basically I don't want the female protagonist to be a whore. (At least not initially)
It always feels like riding a bike with a flat tire when the backstory right out of the gate is that she's fucked half the town, where am I supposed to go from there? Fuck the entire town?
Gradual corruption is definitely something that gets my juices flowing.
A fresh "young" (late 20's-early/mid 30's) housewife is good too but if I'm honest there's nothing on this God forsaken planet that beats a pure maiden or cute school girl.