Should I use a subdomain for blog page?

I am trying to include a blog page in my e-commerce site. The content of the blog post would mostly be spun or copied content. I am confused if I should or should not use a subdomain structure for my blog.
What might be a better choice?

Code:
mystore.com/blog

Or

Code:
blog.mystore.com

Are they any pros/cons for one over other in SEO perspective?

Thanks