I my opinion, the one piece steel mounts are the best. Here's why:
Two piece steel or aluminum (sp)seem to magnify the harmonics (vibrations) of firing the weapon. The harmonics radiate through the front ring, then radiate through the scope to the second ring before leaving the rifle. Aluminum is very porous and vibrations are greater than steel.
When a single mount of steel is used, the majority of the harmonics radiate through the base and is minimized through the rings and scope. I remember reading in this forum of someone having trouble keeping a zero on a rifle. This may ans the question.
hjn