Take radio station for example. Every station claimed to be the best themselves. Does that count as false advertisement?

If every station claimed to be the best, then who exactly is the best?

Can people sue them over false claim? But against what kind of proof? 

If they can say, it's subjective. Then does that mean anything said would be considered truth, since it is subjective?

/nonesense 

Note also, there are different things you can be best at. Just thinking off the top of my head, one of the three "adult pop" radio stations from back home used to use the slogan "Best mix of the 80's, 90's, and today." One competitor plays 70's music as well. Another only does 90's and on. So they're completely accurate. The other battle was minutes of music vs. advertisements. One station would say "we play 50 minutes of music for every hour," while the competition says "we only play 5 minutes of advertisements for every hour." The second station, however, does a lot more DJ talking in-between songs, and the DJs do plugs and promotions, but they're only counting actual "commercial" advertisements, so what they say is true. But the second station only plays 45 minutes of music for every hour.

But in the end, nobody lied.

Is this an American thing? Because I couldn't really care less if 2 companies said they were the best. Best is a vague word anyway.