Which one would be beneficial from an SEO perspective?

[Kaltiro]

I am now considering starting a new project, and I plan to build its infrastructure using Blogspot. But I have a question in mind. Let's say I want to purchase the domain abcd.com. Should I link this domain to Blogspot as abcd.blogspot.com, or should I use abcd.blogspot.com as a dummy blog and get another extension like xyz.blogspot.com to link it to abcd.com for SEO purposes? Which option do you think would be more beneficial in terms of SEO, or does it not matter?