Interesting study was done by the NSCA and posted in there journals. They wanted compare the two different modes of training. Short Sprint Training 4 x 50m or Long Sprint Training 200m at 85% maximal effort to increase anaerobic and aerobic capacity. The practical application is that both were relatively the same in enhancing both aerobic and anaerobic capacity. We will still give the nod to short sprint training for increase speed and agility.
For the soccer coach I would recommend mixing it up between the two to keep the athletes enthusiasm with new training methods.