web forwarding vs domain mapping

Hi,

I own a domain which points to shopify, and 2 separate subdomains of that which are the urls for 2 wordpress blogs I run. They physically live on the domain, but must have different urls as the domain itself points to a shopify domain.

All works fine, but when I was looking in my domain account yesterday I noticed that one subdomain uses web forwarding to achieve the result, and the other subdomain uses domain mapping.

Like I say, both achieve the result, but which is best for SEO? Should I make them both use the same method? The aim would be for Google to view the domain, and both subs as part of the same domain (despite their complicated back ends!).

Thanks