For an important decision, such as a tenure case, it might be reasonable to use all of them. For an annual or biannual salary review it is more reasonable to use one or two. Course evaluation surveys from current students. Easy to do. Gives immediate feedback to teacher.
Students are evaluating events in the recent past, so they have good recall.
Tends to reward entertaining or flashy presentations rather than straightforward yet valuable ones. Discourages innovation, because students usually rate highly the teaching formats that they've seen before. An important point concerning student course evaluations is the need for a variety of evaluation forms for a variety of course types. For example, the Oberlin Physics Department uses different forms for lecture and laboratory courses. Teaching evaluation surveys from course alumni.