Both.

    - The font needs to download
    - The font might not download at all

Browsers support these wonderful two defaults called `sans-serif` and `serif` that will use a default, system-installed, user-controllable font that doesn't need to be downloaded and will be guaranteed to work for any user!

{ font-family: sans-serif; serif; }

You don't even need to use css at all to make text visible on a page.