Generally the way it works is as follows:
Monday: International flights for business travelers and consultant commute day-- increased demand
Tuesday: Normal day
Wednesday: Normal day
Thursday: International flights for business travelers and majority consultant commute day and begin weekend travel-- increased demand
Friday: International flights for business travelers and straggler consultant commute day and weekend travel-- increased demand
Saturday: Weekend travel and international flights for business travelers-- increased demand
Sunday: Weekend travel and international flights for business travelers-- increased demand
That applies to US domestic flights and many international routes as well. Accordingly, Tue and Wed are the best days to fly when it comes to availability of any space, be it revenue, upgrade or award. There are always exceptions based on events or possibly specific routes, but I think virtually everyone in the travel industry and most experienced posters here will tell you that Tue/Wed is the rule of thumb unless there is something else to go by.