the body of the fastback isn't as solid as the coupe back. so as far as structural rigidity goes..(important for drifting) the standard S13 wins the prize
in case your wondering WHY its not as stiff...the coupe back drops down to the frame sooner and has better bracing. the fastback is sort of like a hatch, where it doesnt connect till the rear. this is why the new 350Z comes standard with a strut tower brace in the back.