None, it’s entirely up to you and what your personal preference is. Personally I prefer to use non-WWW as it makes the URL shorter.
However, regardless of which one you decide to go with you should do some SEO tweaking and set a preferred domain.
You should redirect (permanent or 301 redirect) the non-preferred domain to your preferred one. Because search engines consider URLs with and without WWW as two different websites.
A basic Google search for “how to redirect www to non-www” (or vice versa) should point you in the right direction.
Cheers and good luck!
