Forwarding zone or Delegated zone in DNS servers? Which is better for F5 DNS?

Your pc sends a DNS request to your local DNS (LDNS), and that server will do all the work for your pc. So, if it is forward or delegation, it will be transparent for you, and GTM. For GTM, does not matter how the request arrived there.

Delegation is used when the GTM will use a subdomain of your domain, like wip.example.com (example.com been your company domain). You must use forward, when you are using something different than your domain, like wip.local.

That said, they produce the same result.