hyphen looks better in my opinion.. it will be a useful feature for those who will set up a new forum from scratch. For example, in most used blog software, there are options to set different seo url formats..
SEO URLs end with dot.. Nice but. Add the option to the admin panel, replace dot with hyphen
For example:
https://xenforo.com/community/threads/where-to-obtain-support-for-third-party-add-ons.92672/
replace with...