What is the difference between Pulsed Dye Laser, Ng: YAG laser, Cynergy Cynosure, BBL in terms of treating redness in the face?

It’s far better to consider the experience and expertise of the doctor you select than the device used. A board-certified dermatologist with expertise in laser treatments for diffuse redness will be able to tailor your treatment to your precise needs and skin tone to achieve the best possible results. I personally prefer the Vbeam for many of my patients, which is a pulse dye laser. However, there are other options to consider as well. As long as you are working with a qualified provider, you should expect to see a good outcome from your treatments. 

there are many treatments for redness, what matters most is whos hands its in.  in my opinion yellow laser and excel v are the best for diffuse redness, pulsed dye/v beam is great for vascular birth marks, and aerolase and yellow laser for telangiectasias.  Light stim should be used weekly.  Best, Dr. Emer.