Our friend Rabbi Yitzchak Blau points out...
In all educational fields, we should be careful not to identify the best teacher with the most popular teacher. All things being equal, it is certainly a good thing for a teacher to be liked. However, popularity can be achieved in all kinds of educationally dubious ways. A teacher can achieve popularity by going too easy of the students, telling them inappropriate jokes, always siding with them against the administration and by encouraging them to adopt an arrogant attitude that only in their classroom is the truth being taught. Yet all of these methods ultimately hurt the educational process. Apparently, popularity and quality teaching remain distinct categories.And all this based on the Gemara Sotah 40a!
Read Yitzie's analysis of an aggada here (and view the archives of his series on aggada here).