I work 32 hours, so I have one extra day off each week.
If you asked people which day they would like to have off, a lot of them would probably shout Friday. Because then your weekend starts nice and early.
But those people are wrong.
The best day to have off, at least for me, is Monday.
If I had Friday off, I would not want to do anything that day, because it is finally the weekend and the weekend is already fully planned anyway.
Saturday is always for football and social things. Sunday at home is for rest and family.
But if you put your day off after the weekend, you suddenly have an extra day to be somewhat productive. By then I am already nicely rested and ready for a new week.
On Mondays I usually potter around the house, read a book at my own pace and fire up my PlayStation if I am properly into a game again.