This is usually bad for SEO. I've seen it myself, even same content on subdomain will fail to gain SEO.
You are better off doing domain.tld/website than website.domain.tld
I've seen none of my subdomain rank at all, or if they do, they rank poorly. Do me a favor, and search tor-relay-1.innonetlife.com. Last I saw, nothing comes up. Now search innonetlife.com. Second result. We've even submitted a sitemap for the subdomain
Also, the way our site is set up,it should always redirect to the "www" subdomain-but Google never shows it
See #5 here
Also, the less typing a user has to do to get to your site, the better. No one would rather type subdomain.domain.com than domain.com.
Of course, SEO is more than subdomain vs domain - it's about links, quality content, etc. If you don't have good indexable content, this entire discussion is pointless. If you wish to reformat a question for general SEO (hopefully,not a duplicate), I can certainly give some pointers.