Thank you very much.
Joseph
A: Hi Joseph - I'm going to answer this question and your three previous ones with one post. Long story short, SEO is more art than science and I'm a novice in the discipline, not a grand master. My advice on how to get readers to your blog starts with publishing unique and relevant content within a relatively narrow and consistent topic area. If you're doing that, do it every day and keep doing it for a while, you'll start to see the traffic and readership you're looking for no matter how you set up your domain.
That said, as long as Google includes the URL of your page in their results, you might as well make your URL structure as specific and reader-friendly as you can. So if your URL is a compound three letter wor, both crawlers and humans are going to be able to understand the "three_letter_word" format more accurately than they are the "threeletterword" version.
On the topic of top-level domain vs. subdomain for your blog, I've always thought that the cleaner and shorter your URL, the more likely users are to trust your site and perceive it as a high-quality destination. By that logic, three_letter_word.com would be more "trustworthy at a glance" than three_letter_name.three_letter_word.com (or three_letter_word.com/three_letter_name.htm, for that matter.
Hope that helps, and thanks for using Askablogr!