Should the Router or Firewall Come First?

Network scenario…. I have a typical enterprise network meaning ISP>>>>Edge Router>>>>>Firewall|DMZ>>>>Switch>>>LAN.

I know there are several debates on the internet about what device comes first but based on a typical medium size office 500 people, what should come first in the network architecture, the firewall or the router. My thought was that the router should come first because the IOS firewall would be the first line of defense, then a Palo or Sonicwall for the firewall would come next to take whats left. Let mw know if you think im wrong.