Ever heard the saying "Speed Kills"?
You are only born with speed, but strength can be gained by lifting. Since you can't dramatically increase speed as much as strength in the weightroom, the nod goes to speed b/c you now have the potential to be fast AND strong.
In example, if you're like Arnold, you were born strong. Arnold, no matter what he does, will never be able to run a 55 second and under 400m dash. Arnold, however, can bench say, 550lbs.
Carl Lewis can run a 400m in say, 46 seconds. Theoretically, if he wanted to, he could probably build his bench max to 400, whereas let's say he can bench 225 now.
All in all, speed is something you're born with. You will never get dramatically "faster"(sprint wise) no matter how many wind sprints you run during your time on the track. On the other hand, you can dramatically increase your endurance and strength while still retaining your speed, though there is that break even point where too much muscle mass = drop in speed. Ideally, you want to max out muscle mass without sacrificing speed.