Best and most effective laser for thick dark beard?

You are correct. Light skin and dark hair are ideal for laser hair removal.  There is not one brand/laser that is better than another.  In the hands of a competent laser technician there are several lasers that would be effective.  It really is the preference of physician to determine what brand of laser to use.  In our office we use the lumenis 810 diode for most skin types and a 1064 NDyag for darker skin types. It would not benefit you to be treated with  a laser that is not appropriate for your skin/hair type.

You have the perfect contrast for laser hair removal. Based on your skin type and hair color you are a good candidate for an Alexandrite 755 or Diode 810. These wavelengths will get you good results but this also depends on the specific technology or make of laser. I would recommend a Clarity Laser which is a dual wavelength and can treat all skin types effectively.