The median is most likely to be meaningful:
The average is distorted by the single very high salary, and so is not a good measure of the 'typical' salary
The mode is not meaningful. Two salaries are the same, but this could be either coincidence or two employees on the same grade
The median is the best measure for this example
Note:
the data set is unrealistically small, but I just want to illustrate the point
the answer is the most likely, I can think of some purposes for which the average might be most useful