WWW or not WWW, that is the question..

In the dim and distant days at the dawn of the web, those publishing a URL on offline media would add the ‘www’ prefix. It informed everyone you’d moved into the twenty-first century and owned a piece of prime real estate on the World Wide Web.

Fast forward to 2012. Everyone knows what the web is few organizations publish their URL with a preceding www. People understand that Google.com, Facebook.com, Twitter.com etc.. are websites.

Obviously, the first rule for site that work with or without the www. For the sake of SEO and canonical/duplicate content issues, you should choose one domain option and redirect when the other is used.

but my simple question is: what is the best choice? and this choice have or not have influence on the seo..

It doesn't matter - use whatever floats your hovercraft.

Actually the www is part of the URL; it is the name of the server.  However, one has to remember that it is not the domain name that is used to direct web traffic but the IP address.  Therefore, it can be set up to use the name of the server or not; this is done in the DNS server.  In the case of my web server, I look for both the www.domain_name.tld and domain_name.tld.  While we often see www.my_domain.tld, we could just as easily see sally.my_domain.tld if the server name was sally.

Usually it is set up so that either www.my_domain.tld and my_domain.tld will both resolve to the same IP address.

And no, use of www or not does not affect SEO; fresh content is one of the biggest factors in SEO as far as google is concern, bing may be different on the fresh content

www is not the hostname, it's a subdomain (albeit usually linked to the main web directory).  It's also uncommon for a site to be served from the hostname (e.g., server1.example.com).  The hostname is the server's actual network name - unless someone at the data center likes to call the server Bob for some reason.

Edit: I mean the server's hostname, if that helps.

No, the www is the server name, or host name, not the sub domain off of the domain.  http://www.sub.domain_name.tld would be the fully qualified domain for a sub domain using www.

A lot of hosting companies do name the servers using many different protocols; some use planets, some use animals, etc.  In order to log into your control panel, one must must know the server name.  For example, Arvixe names their servers at one time based on animals.  So maybe you would have to go to hippopotamus.arvixe.com in order to log into your control panel.

From Indiana University:

What is a fully qualified domain name (FQDN)?

A fully qualified domain name (FQDN) is the complete domain name for a specific computer, or host, on the Internet. The FQDN consists of two parts: the hostname and the domain name. For example, an FQDN for a hypothetical mail server might be mymail.somecollege.edu. The hostname is mymail, and the host is located within the domain somecollege.edu.

In this example, .edu is the top-level domain (TLD). This is similar to the root directory on a typical workstation, where all other directories (or folders) originate. (Within the .edu TLD, Indiana University Bloomington has been assigned the indiana.edu domain, and has authority to create subdomains within it.)

The same applies to web addresses. For example, www.indiana.edu is the FQDN on the web for IU. In this case, www is the name of the host in the indiana.edu domain.

Only if you set it up that way. www is nothing more than a sub domain and it is rare for a provider to use the actual name of the server as a web address. In fact, all names proceeding the actual domain name are sub domains. Including the host name that was given to the server.

Back in the day when i was a internet service provider, i also did hosting. This was back in the day when dialup was king and Big dick company's like Verizon and Comcast stayed out of the internet business.

All of my servers were named after gods from greek mythology. Like apollo.mydomain.com, ares.mydomain.com, or athena.mydomain.com.  Naming a host www vary rare.

 
Oh, now i get it. You getting your information from a university which does not do things the same way as the rest of the world.

However the article does state that their domain is indiana.edu and they have the authority to create sub domains within it.

So saying that, it is 100% correct to state that www is a sub domain because it is. and www.indiana.edu is a FQDN which it is. And www is a subdomain which it is.

Where the confusion is occurring is with the definition of host. And this is where universities differ from the rest of the world.

A university typically runs only one service on a server. FTP on one server, web services on another, dns on another, ect. So to them, the name they prefix the domain with is also the host name and even the name of their server in many cases. University's typically also use multi level sub domains such as ftp.red.crab.indiana.edu which the rest of the world rarely uses.

To me the sub domains represent a service, not a host. The host is the server that hosts the services running on it. So in essence prefixes of www, ftp, pop3, smtp, mail, ect are all services that in many cases are run on one host/server.

Most people do not follow the same set of rules that universities follow so it is my belief that their definition of host in their article is incorrect.