Behind this obviously subjective question lies the philosophical axiom, “A taxonomy is never innocent.” What this means is that any judgments, any ranking, and categorizing of elements must begin with an understanding of the motives of the taxonomist, what criteria are given precedence over others, what values are being placed on each element in the group. If one were to rank food, for example, ice cream, cookies, candy would rank high if the criterion was immediate pleasure gratification; if the food were ranked by nutritional value, then vegetables, lean meat, fish might be “better” than ice cream or cookies. If the criterion is preservability, the foods would be ranked another way. In your question, then, the first step is to define “better.” If we are speaking of leisure time for the average adult, we might easily say Saturday is “better” than Friday, but if we are speaking of getting to the post office or the bank before it closes, we might rank Friday higher, since the post office closes at noon on Saturdays, and the bank is not open at all. So, underneath you innocent question is the essential element of ranking—set out your criteria clearly before you begin to rank things.
Saturday is better because there's more free time compared to Friday. On Friday there is still school to attend, but on saturday we are fee for the whole entire day.
Saturday is better because it means no school at all whereas friday there is still a day of school so technically the weekend starts when you end the school week. Also...my schedule ends on those days.