How to differentiate a great company to work for from a good company to work for ?

There are five or six things areas that define whether a company is good or bad to work for.  Salary is one, whether the company is successful is one, whether they provide good training and equipment is one, and so on.

A good company to work for will be at least average in all of these areas, and above average in one or two.  A great place to work is where they are all well above average.   This is very rare.