It goes 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 always more favorable.
Don't make excuses for shortcomings. Instead, point to your strengths.
At IBM, we followed this same principle. We were not allowed to talk down our competition. We could acknowledge them and their products, yet we never put them down. We were required to sell IBM on the strength of IBM, not on the weakness of others. Our customers appreciated our willingness to accept the competition and seek to rise above on our own 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 the 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, but 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 fifteen to 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.