Short or branded for free subdomains assigned to user?

So we all know many website making services or blogging service provides free subdomain for users (like myblog.wordpress.com for WordPress.com). But should we give users branded subdomain like WordPress which will be long and bulky? Or short domain like myblog.wp.com which is short while still some way branded? Or even username.blog.io (which clearly impossible), but which mean the main domain is topic-focused but not branded? Which one should I choose for users' free subdomain as a free blogging service? Since you'll need to consider not all the users are getting traffic from Google (where URL doesn't matter much on SEO). Some user might share the url directly to their friend, or parents of students, which they might want a shorter url.

Or I should have a long-branded domain while also get a service-wide URL shortening service?