Answer
The median is best because there are some few people whose net worth is high (very high for some) and these high net worth values affect the mean a lot, but not the median.
Work Step by Step
Take for example 9 people, each of them with a net worth of 100 thousand dollars. If you put among them one person with a net worth of 1 billion dollars, their new mean will be about 100 million dollars, but the median remains equal to 100 thousand dollars.
