V beam or Nd Yag laser for red acne scars and brown hyper pigmentation that appears following an acne lesion?

The best lasers are vascular lasers for red acne scars. This is either the Excel V or Vbeam laser. This will sometimes take care of the PIH. If further therapy is warranted, a Q Switched 1064 laser with low fluence can help the brown. Chemical peels and topicals such as Retin A and hydroquinones are helpful too.

The pulse-dye laser is best for red/pink scars. Brown hyperpigmentation can be addressed with either chemical peels or Nd:Yag laser, depending on your skin type (color) and how long you have had the hyperpigmentation. None of those treatments are known to thin the skin, but you should consult with a board-certified Aesthetic Dermatologist for a complete scar evaluation.  

I prefer the V-Beam laser for the type of acne scars that you are describing.  You may also need some bleaching creams or peels to remove the hyper pigmentation.  Sometimes a combination approach is best.