Hello, If I have a site on green barnacles, there is obviously not a lot of competition for that niche. So if I want to rank my page at the top and have done all the necessary SEO on said page, would there be any real reason not to go with greenbarnacles.otherwebsite.com versus greenbarnacles.com if Google sees otherwebsite as an older domain and has it ranked highly for another, competitive niche? What I'm trying to avoid here is google sandboxing for greenbarnacles.com and I'm also trying to gain from the site being a subdomain of a trusted / old domain. Any thoughts/comments greatly appreciated and +rep given. Thanks!
With the proper optimization, it shouldn't matter if you're using barnacles.com/green or green.barnacles.com I would actually prefer the subdomain in this case because it would make more literal sense. If you didn't want to use a subdomain, I would say do something like: barnacles.com/types/green or something similar.
It DOES matter because they are treated differently by Google. A subdirectory gets the full authority of the entire site, a subdomain is treated almost like an entirely new domain.