Originally Posted by
GearHeaded
depends mainly on GENETICS and muscle fiber type your body and different muscle groups possess.
example
Phil Heath - he has always trained primarily with machines for every body part and always has (he's had no injuries)
Ronnie Coleman and Branch Warren - always trained with free weights and big heavy compound moves (lots of injuries)
Both work dependent on your genetics . Phil heath probably is a genetic freak possesses a whole shit ton more sarcoplasmic muscle fibers then most guys (sarcoplasmic fibers hypertrophy very well with machine pump work and respond well to steroid use).
Branch Warren on the other hand grew very well using heavy weights and relied more on Myofibrillar hypertrophy (heavy weight low rep) . he is probably more myofibrillar fiber type dominant.
I advocate a good mixture of both , BUT when natural and building your base I always recommend doing the heavy compound free weight lifts as your primary workload (squat, bench, deadlift, overhead press, bent over rows ,etc.)