Waianvil, it depends on what you are going to use it for.
1. bench vise, for filing, twisting and other hand work. standing beside it with your arm down by your side and bent up at the elbow, your elbow should just rest on top of the jaws.
2. pounding anvil, close to the anvil and used for a lot of hot work. Same height as anvil or about 6 inches taller.
Like anything else you must decide what you are gonna use it for the most.