Another one to forget about. Sometimes I use directories and sometimes I use files. I have not been able to determine if there is any actual benefit to using either.
I prefer files like .html when I am building a new site from scratch, as they are the ultimate end of the line for search engines as I visualise things – whereas a folder is a collection area, wether you have other files apart from the index or not. I think it takes more to get a folder trusted than an individual file and I guess this sways me to use files on mosts websites we design, though that’s the first time I have really thought about it. Once folders are trusted, it’s 6 or half a dozen.
Folders can be treated differently than files in my experience. Some folders if you don’t linkbuild or incorporate into the site archiecture properly can be trusted less than other folder in your site or ignored entirely. Folders seem to take a little bit longer to get indexed by Google than straight files in some cases.
People talk about trusted domains but they don’t mention or don’t know not all the domain has the same amount of trust. Google treats some folders….. differently. Probably dependent on where links are coming from – is this folder starved of links when the rest of the site has hundreds? Google might take a while to get to know it.
Some say don’t go beyond 4 levels of folders. I haven’t experienced too many issues, but you never know.