if DHP is used

Clarifications

I like a router to do routing, and a firewall to do firewalling, so I'd put the DHCP function on a server.
From a security perspective, an attacker hits your outside router or your firewall first, so if that's compromised they now own your DHCP as well. Put it on a server and it's one more layer to penetrate.
From a management perspective, both Windows DHCP and the Linux dhcpd (via Webmin) have pretty GUIs, so you can manage DHCP a little easier if it's on a server.
And from a reliability perspective, I believe that both Windows 2012 Server and dhcpd support true redundancy in DHCP.

but that kinda sounds like homework

I prefer it on a server also. With Server 2012 it's very simple to setup a highly available and redundant solution.