The mean is the better for center when the dats is symmetrically distributed like a normal distribution. The mean would be the best one to use in the following set of data. 1 2 3 5 6 7 8
However if the data is not symmetrically distributed ( there are one or more 'outliers; ) then the median is the better choice
For example 1 2 3 4 7 8 11 39