How to judge the reputation of a potential advisor or research group for good quality research for PhD? I am planning my PhD and am applying to various labs and professors. 

I am getting positive responses, but I am having trouble making a decision as to which lab to go for. How can I judge the quality of research of a group? What parameters shall be kept in mind while making a decision? I usually look for relevant research interests.
How can I judge the quality of research of a group?


This is the wrong question.

What you should be asking is "How can I judge which research group will best support my educational and career goals?"  And yes, this is a very different question.  And while lab productivity may be correlated with the future career prospects of its members, the two are not identical.  Some great researchers are terrible advisors.


Are the lab's students happy?
Do the lab's students have a consistent strong track record of publishing new results?
Are the lab's students strongly represented at conferences, workshops, and the like?  In particular: Are the lab's students given ample opportunity to present their research outside their home department?
Are the lab's students given ample mentoring and support, both in developing their own research agendas and in applying for external fellowships, lab exchanges, internships, postdoctoral positions, faculty positions, and so on?
Are the lab's students given ample opportunity for substantial intellectual contributions to the lab's published research, or are they just lab/code monkeys?
Does the lab's research agenda closely match your own research interests and abilities?
Most importantly: Where do the lab's former students work now?  (The worst possible answer is "We don't know.")


Almost none of these questions can be answered accurately without physically visiting the lab and talking directly to the students without the PI present.  If travel is impractical, use Skype / Google hangout / Facetime / whatever.  Or telephone.  Or, if all else fails, email.