Answer: One area
Step-by-step explanation:
It is best to be great in one area than to be mediocre in multiple areas. If you are really good at something, it is best that you focus on that thing so that you can push that field forward such that you can be known to have added to the advancement of that field.
This is better than being average across a couple of fields which means that you are way less likely to improve those fields. For example, if Einstein had not focused solely on physics and the sciences but had rather gone into finance, law, and other fields, it is very doubtful that he would be the household name that he is today.