The answer is Testimonials because the singer is giving a testimony by saying the station is the best.
It could not be facts or glittering generalities because those do not involve people.
("In promotion and of advertising, a testimonial or show consists of a person's written or spoken statement extolling the virtue of a product. The term "testimonial" most commonly applies to the sales-pitches attributed to ordinary citizens, whereas the word "endorsement" usually applies to pitches by celebrities. Testimonials can be part of communal marketing. Sometimes, the cartoon character can be a testimonial in a commercial.") from Wikipedia