It should go without saying that talking down the competition is a no-no. But talking about the competition can be quite different—if handled appropriately.
When Abraham Lincoln was arguing a case in court, he would usually argue both sides of the case to the jury. He would first take the opponent's side of the issue and then his client's side. But note: he was always very precise in bringing out more favorable facts for his client than for his opponent. Both sides were covered on a positive note, although his client's side was covered more favorably.
IBM is noted for following this same principle. IBM salespeople are not allowed to talk down the competition. They can acknowledge the competition and their products, yet not put them down. They are required to sell IBM on the strength of IBM, not on the weakness of others. And IBM customers appreciate the willingness to accept the competition and seek to rise above on merits rather than try to push the competition down to a lower level. So if you are confronted with a comparison to your competition, be prepared to fully acknowledge the strength of your competition, then follow with what you feel are your own greater assets.
An example in applying this technique is how to handle the potential negative when the interviewer asks why you are lacking in a particular area (be it grades, work experience, extracurricular activities, etc.). You need to first speak well of others. Then you need to establish your own case, which can also include using the Reframing Technique. An example would be in response to a question about a low GPA:
"I'm sure that there are many who have put more time and energy into their GPA than I did—and I congratulate them on their efforts. Grades are important, yet my overall focus has been to develop myself as the very best accountant I can become. For me, this has involved not only time in the classroom, but also time in applying these skills in real-world situations. Because of that focus, I have spent twenty hours per week working as a bookkeeper during my final two years. While I was not able to devote myself full time to pure academics, I feel the combination of academic and work experience has more fully prepared me for the accounting field than full-time academics alone."
Honest Abe would be proud of you.
In addition to not talking down your competition, avoid any kind of complaining. Complaints always leave a bad and unnecessary taste in everyone's mouth. Think about the family dog (whether or not you had one growing up). Everybody loves the dog, except when he smells and needs a bath. Same with interviewing. There have been countless interviews where things seemed to be going just fine, until the candidate begins a series of complaints about others. And the spotless candidate has suddenly become hopelessly stained.
Is there anything worse than a complainer? Nope, nothing worse. We all know one, and we all want to distance ourselves from that person. Company or otherwise. So remember that the interview is not your forum for griping. If you gripe about your current or past employers or professors or college or make note of any shortcomings in your life or missed expectations, you have just relegated yourself to the role of "complainer." And complainers are all too common already within most companies. Don't play the blame game. Why would any company hire a complainer? They won't. Be positive about everything. Case closed.