I prefer doing more shorter sprints. I usually end or start with a longer "fast" run though. I do something like a track workout, or "speed", so far its helped with my legs explode and has helped with overall stamina. Plus I run faster.
Something simple like:
You do decent yardage, but its all high intensity and short distances that wont kill your knees or ankles.
Also I like to mix it up with some sled drags, build-ups, mt.climbers into sprints, bearcrawls, etc.
Sprinting is really an effort thing. If your honest then it'll kick your ass and make you feel good (as in puking).