I vary my days off to suit whatever else I have on but Saturday is the mainstay of my working week, sometimes I do 9 or 10 hours as opposed to 3-5 hours Sun-Thur or 7 hours Fri so if I take a Saturday off it'd be my only day off whereas I can take any other two days off. As you get older and less fit it helps to take two days off together if you can. This year I've been mostly taking Wed/Thur or Thur/Fri off, except for the odd lazy week.