Everyone is very much familiar with 'www', the word preceding any domain name. As it was used to direct an application to the right service like web, mail, ftp, etc on the right server.
Here is the question is whether to continue applying 'www' before the domain name or not !
As nowadays, there is no a strict technical requirement to use 'www' to direct the server, as it was use earlier to direct an application to the right service. Many people who are associated with it like site publisher, will suggest you not to apply www. and stick simply to "website.com".
If you ask me I will suggest to use www. as it gives your domain some viewable symmetry that balances with the .com suffix.
Whatever you follow the url structure for your website, the main important thing is, stick to it. Sticking to the one format of the url will help you to brand your website, but also it will better your search engine ranking as search engine count www.website.com and website.com a different website.