Speech.

> Television and radio stations need to abide by FCC guidelines

As far as the content restrictions, they only need to do so if they are broadcast channels (or cable rebroadcasts of broadcast channels), and FCC is constitutionally prohibited from regulating speech on cable-only channels. The argument for why they can do broadcast is the "compelling government interest" in policing the inherently limited broadcast spectrum, which (quite frankly) is pretty shaky precedent if you ask me.

> Another example: Tobacco advertising is severely curtailed

Advertising is commercial speech, which the government has much more powerful abilities to restrict than expressive speech.