He is a world-class, top-tier pianist.
This hotel provides first-rate service.
This company possesses top-class technology.
最高級 describes the highest grade of a product or quality, whereas 超一流 is used more for people, companies, or skills being top-tier.
三流 means 'third-rate' or 'mediocre', the direct opposite of 超一流's 'top-class, elite' sense.
Compound of 超 (chō, 'super-') and 一流 (ichiryū, 'first-class').