High mass vs Low Mass Turntables - Sound difference?

Either design can sound good as evidenced by Regas and the numerous mass loaded designs. All turntables color the sound to some degree. It really comes down to build quality and personal preference. I personally have a psychological aversion to spending $3k on anything as light as a Rega. However, I'm sure many of them sound great. 

I have had modest benefits using various sorbothane footers with turntables. I suspect they are more effective at blocking transmission of sound from whatever the turntable is sitting on than in reducing mechanical vibrations in the turntable, from the motor or platter. However I have found far better results applying small ( no dimension in excess of 1 inch) pieces of sorbothane to the body of the turntable. These need to be glued using the 3M self-stick which some sheets come with. I use a Lord industrial adhesive when I cannot get self-stick. This is however expensive and hard to find. I recommend thicker sorb, 1/4 to 1/2 inch and denser 70 duro.  Sorb's claim to fame is converting mechanical energy to heat, so it really seems to be getting rid of it. 

Viscoelastic materials like Sorbothane convert vibration to heat ONLY if they are constrained. That’s why they call it contained layer damping. Sometimes there is a thin layer of aluminum On top of the viscoelastic material that constrains it. The vibration in the one direction, e.g., vertical direction, produces shear forces in the orthogonal (e.g., horizontal) direction in the soft constrained layer. So it would not actually make sense to attach Sorbothane to anything without constraining it, since the shear forces are due to the fact that the Sorbothane is being constrained. It does make some sense that Sorbothane used as footers (or as insoles of running shoes) since the component or speaker or person’s mass will act as the constraining mechanism. I gave up on Sorbothane myself a long time ago. As I opined recently there are much better materials to use as the constrained layer. But more power to anyone who gets good results with it.

Good comparison but why limit your choice to either A or B?  These two approaches have taken their turntables to their scientific limit. 
"audiotroy"  is on to it.
Enter George Merrill/Robert Williams and the Merrill-Williams R.E.A.L. 101.2 Turntable. http://www.realturntable.com/product-overview.html
Easily eclipses most anything at any price.  The science involved in this system approach addresses all forms of energy management and speed control.
Mr. Merrill has made turntables since the late 70's and he currently makes 2 budget turntables.  The "PolyTable" turntable starts at $1595
http://hifigem.com/polytable.html
The second is the "PolyTable SUPER 12" at $2995 both with tonearms
http://hifigem.com/PolyTableSUPER12.html  This table easily competes with the likes of the $10,000 crowd!
Just the facts here and I have no financial interest in any of these products...
Happy listening!

No one is suggesting there has to be a choice between high mass and low mass designs. Those are just design concepts. There are obviously a lot of variables and parameters involved. Mass is only one of them. You got your spring and unstrung designs. Belt drive vs direct drive. Tangential vs radial tracking. Vacuum hold down. What have you. And there are a great many successful turntables including magnetic levitation and air bearing everything that tend to actually eliminate the whole variable of MASS. The best way to solve for a set of simultaneous equations in many unknowns is start eliminating the unknowns. Obviously also, not matter what design concept is employed in a turntable the performance of that turntable can be easily and reliably improved by vibration isolation. I don't think any list of great turntables would be complete with Linn, Walker, Maplenoll, Verdier, AC Raven, Caliburn Continuum, VPI, SOTA, Basis, and a bunch more I probably forgot.