This may sound obvious, but a good program is one where you will be happy doing research. This means that you like the research that is being done there, and that you have a supervisor (or potential supervisors) who is supportive of your work and will help you develop as a researcher. 

 Other things to look for: 

1. Does the department have other students in your area of interest? Being able to bounce ideas off others will help your progress enormously. 
2.  Is there funding available? If they can’t pay you, or give you money to present at conferences or do fieldwork, then it’s probably not worth going there. 
3. Will there be opportunities to teach? This can be a good way of getting experience if you want an academic career, but if not it’s probably not worth doing.