Using www.domain.com is better for SEO than using domain.com But what about www.sub.domain.com and sub.domain.com?
there is not much diff with that no one use because it makes leghty and looks ugly. also to avoid typo errors
I agree with chadlan, once you get down to subdomains, www is just to long and a waste. It really wont make much of a difference which one you use.
For SEO keyword targetted domains are best. Don't worry too much about www any more BUT just make sure you are consistent with your linking strategy. So if you decide to use www.domain.com - make sure you stick with that for all your links (or choose domain.com) but don't mix them. Sub domains are handy for things like targetting local markets of your niche eg ny.myflorist.com, houston.myflorist.com - where it's much easier to forget about the www
i agree with seafrontsteve. just target your keyword for seo. the best is your domain contain your targeting keyword
Canonical domains and non canonical domains rank exactly the same in Google and other search engines, I have tested both and it just comes down to personal preference. Sub domains however are treated as another domain other than your existing domain, so I would assume they would rank the same, there are plenty of sites out there you using sub-domains to rank highly for very competitive terms.
that's not different, sub.domain.com is better for visitor to memorize. by the way, you can still redirect sub.domain.com to www.sub.domain.com if you want