IMO it depends on the resort/location...
With Hawaii, where you lose time flying home, I think Sunday is probably worst since many would take a redeye back and arrive Monday morning thus maybe having to take another vacation day. But I don't have experience with renting there.
I know some people like to book Wednesday checkins for Hawaii because it can save on airfare and there is probably also less competition in the rental market. Obviously with Vistana that's a Staroptions reservation at 8 months.
Otherwise, I usually try to avoid Fridays since, in most cases, a Friday-Friday vacation involves 6 vacation days while a Sunday or Saturday weeklong vacation is just 5 vacation days (ignoring holidays and such).