Best Link for Image

Can anyone tell me which is the best option of linking an image and why?

1. Link directly to the media file
2. Link to the attachment post, in which case the file will be served via the WordPress Template Hierarchy
3. Not link to the media file (e.g. in the case of images, the image file will still be embedded in the page, but not linked to allow the browser to display the image file by itself)