Unpopular opinion of mine, my favorite is Thursday. I find that it is the most productive day of the week work-wise because people are so ready for the weekend by that point of the week and are pretty agreeable (especially when I use the "ready for the weekend?" ice breaker in conversations).
Mine is Saturday because it is the day where I will receive lot of bonuses from casinos to enjoy my weekend very well. Also , I go out for outing with my friends on Saturdays.