The correct height for a vanity is the one that you are most comfortable with. In the past 30″ height with the top was the norm. As the years have gone by my clients have asked the cabinets to be raised. We are now at the point where most people prefer 36″ with the top. This height is the same as your kitchen counter.
Custom Cabinets or Stock?
The other consideration before selecting the height of the vanity is to know if you are going to use custom cabinets or stock. With custom cabinets we can set the height at anything we want to. My ideal height is 33″ with the top.
If you are using stock cabinets then you are going to be limited in size to the 30″ height or use a kitchen cabinet and see if they can reduce the depth to 21″ for you.