The choosing of ebgp or ibgp

So in a basic situation where one has two WAN routers, and two core switches... and you are wanting to advertise all the WAN routes from the WAN Routers to the Core, I feel like the best design for this is to choose iBGP. iBGP will not advertise routes learned from an iBGP neighbor, to a different iBGP neighbor.

You do not want the routes from WAN-ROUTER-A to be advertised to WAN-ROUTER-B, and vice versa.

So to me... iBGP makes the most common sense.

But, I have a coworker who is insisting that it is best to use eBGP for this setup, and we can just use a route filter to control what does and does not advertise.

I'm just wondering: why? In this very simple, very basic setup, what is the actual benefit of choosing ebgp, and needing to require extra configuration to prevent the undesired routing advertisements?

Thanks for any pointers you can give!