That would quite obviously be the way that makes you come out on top?
Your only real concern is that inaccuracies cancel out each other. For example, if Runner 1 goes over the prediction by 10 and Runner 2 goes under the prediction by 10, adding them together might seem as though the prediction was perfect, +10 -10 = 0, right? For this cause, it often seems prudent to find a way to avoid this. Most often a square is used, but an absolute value will do the same thing.
(+10)^2 + (-10)^2 = 200
|+10|+|-10| = 20