The Taiwanese FOSS l10n community has a preference for “正體” over “繁體”, but I’m not bothered by either.
As long as you only have two variants, the code is mostly cosmetic. Quite often when the name says “Chinese (Traditional)” the underlying code is still zh_TW. Either way you still need to handle both language-region and language-script-region variants of language tags sent by browsers. AFAIK Firefox on Android does send accept-language with zh-Hant-HK, depending on the Android system locale setting.