Shavers generated power from explosiveness and efficient weight transference, along with naturally heavy hands. Foreman generated power from brutish strength and momentum generated from his long arms and wild arcing swings. If Foreman could land on you he'd do serious damage, which is why fighters who relied on blocking his shots as opposed to moving out of the way tended to get broken down. Shavers was quicker so tended to catch guys unawares and stun them, but if they survived his power they were usually able to come back. In terms of pure power I'd rank Foreman the superior. Shavers's faster hands and tighter technique tended to make him more dangerous as a puncher.