Tooltips above or below the input field?

In Bootstrap and other frameworks, you are able to create and design your own tooltip instead of using the regular title-tag. You are also free to place that tooltip above, below, to the left or to the right of the text input box.

Due to several reasons (Screen magnifiers, the visual focus of the user and so on), there is no reason to place the tooltip to the left or to the right of an input box.

So, where shall one place the tooltip? Above or below the input box?

Could provide me with some pros and cons on these two options: Above or below.