forum.yourdomain.com will act like a seperate domain site. SE will not give credit to the yourdomain.com yourdomain.com/forum will act like one single site. SE will give credit to the yourdomain.com. If you have heavy traffic, better to use subdomain.
That depends on what your goals and objectives are. Search engine spiders will treat the subdomain as a separate domain (which can be good for cross-linking if done properly), but at the same time having a strong forum as part of your Web site by having it in a directory of your Web root can have its benefits as well. Thankfully that's just an opinion. While keywords in domains do have an impact, they are not the end-all be-all that some people mistakenly make them out to be (for the record, when I choose a domain name, I look at making the domain name brandable and easy to remember while sneaking in a primary keyword or two that I'm targeting). But as far as where to place a forum on a Web site, there is no difference and it won't have any impact whatsoever (on its own anyway). Patently false. As I said above, subdomains are treated as separate domains. Meaning that as far as the search engines are concerned, subdomain1.yoursite.com and subdomain2.yoursite.com might as well be the same thing as yourfirstsite.com and yoursecondsite.com anyway. Ayup. There are benefits to doing this though (like i said earlier, cross-linking your subdomains can be effective if done properly), but if the forum is being tied strongly into the main brand, I'd avoid doing it unless I was willing to take a calculated risk on the benefits outweighing the risks. Maybe, but maybe not. It all depends on how the site is developed, where the traffic is coming from and how the forum relates to the rest of the site's content.
Why all this spinning around? Answer the question. This is applicable for SEO marketing. 1. Rule A: use the subdomain only if your domain-name.com is not a popular search word or phrase. Eg. cnn.com: they use subdomains for every aspect of their website -money.cnn.com 2. Rule B: Whenever you use the domain-name.com/forum be sure to extend it to the index.(extension) eg. arcosweb.com/forums/index.php. Without the index.php your robots.txt or meta tag robots fields wont have any effect. This is a very common error I have seen with SEO.
Actually CNN does that because those sections of the CNN site (such as Money) are for all intents and purposes separate sites (with their own unique content and structural heirarchy) that are part and parcel of the CNN network. In this case, having subdomains works to CNN's advantage since they can cross-link those subdomains (or sub-sites if you want to call them that) with each other as well as the main CNN site without having to register a bunch of domain names or confuse people with regard to their location (oh, that's on CNN.com, rather than "what was that link again?). With regard to your second arguement, I highly doubt there's any factual basis there whatsoever. If you have any concrete, independently verified sources (and by independently verified I don't mean your own sites, but outside experts that are widely recognized in the industry for their knowledge and accomplishments) then I might be willing to reconsider that position.
I beg to differ. If you were to explore CNN you would notice a shift in the naming of their website sections, for example, edition.cnn.com/asia as opposed to asia.cnn.com, and there is a site cnnmoney.com. CNN is now a search keyword, but that took years of marketing and seo techniques applied correctly. In regards to using robots.txt and its relation to your index page just read any seo report on the topic as it relate to Web 2.0 resources.
Asia just happens to be a section of the Edition "site" is all, whereas asia.cnn.com would have to cover everything about asia, such as world and regional news, finance, and whatnot. And "read any seo report on the topic as it relates to Web 2.0 resources" does not inspire any confidence in me whatsoever.
yourdomain/forum is better also for readability reason: it can be better memorized. http://www.seo-guru.net
It may be better for you to remember, but not necessariliy others. And what does the SEO-guru link have to do with this discusison anyway?
Go for second one in my opinion: yourdomain.com/forum Note: Try to get the domain depends on your keywords ..
It'll only be better if he wants the content on the forums to be part and parcel of the main Web site. If he wants the forum content to be separate from his main site content in the SERPS, then he should use a subdomain. Of course, such a decision can be made only on a site-by-site basis and has far more to do with information architecture than it does search engine optimization, especially since both have their benefits and drawbacks (which I fondly recall stating earlier in this thread, but people seem to be ignoring whatever I'm saying).