Ask HN: Buy multiple vertical domains or focus on one main domain?

I just discovered that a large pool of .com domains for multiple markets where I could offer a product, is still available and not taken. These domains are similar to this:<p>[Vertical]Mytopkeyword.com BusinessMytopkeyword.com MediaMytopkeyword.com ScienceMytopkeyword.com TravelMytopkeyword.com SportsMytopkeyword.com RetailMytopkeyword.com MarketingMytopkeyword.com AutomotiveMytopkeyword.com ManagementMytopkeyword.com<p>Almost any domain and market with my top keyword is still available. I could basically grab them all in one minute. Should I go ahead and buy like 20-30 domains to cover all these areas direcly, or would it be for SEO a better move to use all these market keyword all together on a single domain instead (as a subdomain) like for example:<p>[Vertical].Mybrand.com or Retail.Mybrand.com or Travel.Mybrand.com ?