Depends on two variables--Supply of beer and/or supply of money. A third variable might come into play depending upon opening hours for beer sales. A fourth variable would be type of beer.

Generally, I drink the last half fastest unless there's a deficiency in the first two variables. In the days when I partied into the early morn, the last beer would be finished real slow. The "koolaide" beers like Bud, Miller, Busch, etc., I olny like real cold, so they go down fast before they cam warm and become like Coors at any temp. But then, I'm certainly not average.