I would like to build a DNS hierarchy with a company-internal
"mycompany.com." domain (hosted on name servers running BIND) and an
"ad.mycompany.com." subdomain delegated to DNS administrators of a Microsoft
Active Directory environment.

I've seen that setting either forwarders (1) or zone-delegation (2) make
name resolution work even for sub-domain hosts:

1) zone "ad.mycompany.com" IN {
type forward;
forwarders {10.0.0.1; 10.0.0.2;};
};

2) $ORIGIN ad.mycompany.com.
@ IN NS ns1.ad.mycompany.com.
@ IN NS ns2.ad.mycompany.com.
ns1 IN A 10.0.0.1
ns2 IN A 10.0.0.2

Even if both works, I think option 2 is best as forwarders are set in
"named.conf" per-server configuration file, while the delegation is set in
the "domain.com" zone file that would be transfered to any secondary (slave)
name server.

What's your opinion?

Thanks in advance. - Gabriele