The Taipei accent is the golden standard of Mandarin in the sense it is the most understandable and spoken by people of the capital. Just like Beijing Mandarin is considered more prestigious than Guangzhou Mandarin. For instance, CCTV on the Mainland uses broadcasters who speak with the Beijing accent. Likewise, Taiwanese broadcasters use the Taipei accent and not the Tainan accent.
I have relatives (regardless of age) from the south who use the “hei” particle even when speaking Mandarin, which I never hear among Taipei citizens. It’s very easy to spot a youngster who is from 外縣市 (other county/city), versus a native. Even though I wasn’t raised in Taipei, I still consider myself a native to an extent, given the amount of time I’ve spent there. My cousins who moved from the countryside still struggle to adapt here, while I just breeze through everything.