If I had a choice between naming a URL www.domain.com/seo.hml or www.domain.com/seo which would be the best choice?
it likely won't make a terribly strong difference regardless. is "seo" an example or what you actually want to use? there are likely better url schemes. domain.com/seo/search-engine-optimization.html for the intro page, for example, then include more under the seo directory.
I would left seo.html or better as disgust said search-engine-optimization.html In some cases .html is better
Actually, they're not different between html page or not but If I were you, I will prefer to .html page.
Well, I think Google would think seo.html is more static and the other one is more likely to be dynamic.
It doesn't make a difference to name your page .htm .html. .php .asp or just domain/topic/ every webpage has the ability to rank in a search engine at a certain position. But I advice you to go into dept.. So that's: domain / topic / more niche topic / content (dot any extension) For instance I've created a page where I describe the directorycontest.com As you can see I've used: domain / topic / niche topic / content.html, this gives a ranking in google search at position 8. But when searching for link baiting you see jimwestergren's page comming to the surface (notice without any extension) And this is actually an interesting search query, the first result is without an extension, the second is a .php and the third result is .shtml. See no difference in extension that influences the search results. The main factor in linkbuilding is this guide from jimboykin. http://www.jimboykin.com/site-backlinks/ Read it and rank
I really don't think it would matter. It will still go down to how you market your site to be on the top list of the search engines.
As I understand it sub domains are looked at by search engines (at least google) as almost a separate site so relevancy, PR, etc wont carry over to the sub domain. IE. it will be really hard to rank if its a sub domain. (unless your sub domain has racks of inbounds) This is not a good option unless you have completely irrelevant information to the overall theme of site.com thus the option to have randominfo.site.com might be warranted.