www or htttp://wwww? Which one is best in SEO?

Well there is no difference between the two. One just has the protocol in front of it, the other doesn't. So depending on where you use it, it will either figure you left it out and auto use http:, or it will error saying it can't find what you gave it (so you should know right away to make sure it is included.

Usually the question is http://www.domain.com vs. http://domain.com

Technically, www.domain.com is a subdomain of domain.com, and most hosting companies will set up both to work the same.

The key there is that whichever you use, you should stick with in all links/posts/etc. (if you know how, do a mod_rewrite to kick you to the preferred one).

-Greg

2. http://www is better.I think .but the two I use too

There is no different between "www" or without "www" in the sense of SEO. It only concern when you purchse SSL to your domain.

You can set up both. The SEO refers only your domain name, xxx.com.

with www or without www can be canonical issue in a single so to solve this issue it is advisable to use only one. i prefer with www is the best one

I prefer the http version as most of my links earlier were http based,and it is easy to track my backlinks in Webmaster tools

If Google can see both, you need to change things so that it only sees one (either one).

That's because, as said above, Google sees these as two different sites, but with identical content.

Google likes unique content, not content copied from other sites, so if it sees both it penalises you. If it only sees one, it like you.

either of the two is fine, though i always prefer using with "www" and if my domain name is really long i drop the "www" , your site success would depend on your marketing campaigns and your strategy

Well, to be honest there is no such different between http://www and www.
It could be discussed if the question is about www and non-www. Although, that is just a technical aspect of your hosting and got nothing to do with search rankings. But they can effect if you have implemented in a wrong way or other than search guidelines.

Thanks.

To google it does not matter. It is only important once you decide on any of the tips is to hold it. That is to link only with the address with www, if you have set modrewrite with www. Or the same oposite situation, if in modrewrite you have only http, dont link to your website with www.

The issue is whether you want the website to be opened with www or without leading www. If any website opens in two modes i.e with [strong]domainname.com[/strong] and [strong]www.domainname.com[/strong]. Then it is canonical issue that needs to be resolved. Otherwise Google sees them as identical websites or copy sites with duplicate content. There is a chance that Google might make the site spam. One can choose to open the website in either of one and redirect to another format by writing 301 redirect in server's ht access file to fix the canonical issue.

Generally people used to redirect www. to http://www. since is the default version suggested by Google. It is only important on how you use it. If you are already using it without www. then just go ahead. If it is a new website, just make a 301 redirection along with http:// and use it by default!!

The OP is asking the differences between "www." and "http://www.". They are the same. The 'http' is the protocol used and you'll end up with "http://www." even if you type "www.".
That said, he probably meant "http://domain.com" vs "http://www.domain.com". It is a matter of preference which one you want to use. Most websites should the "http://www.domain.com" and this is what people are familiar with the most.