I don't like the idea of using a RPi as a router as at least one of the ethernet ports would need to be USB based (or faff around with VLANs and a managed switch into the hard wired ethernet port) and I'd always assume that adds some latency.
Although that's quite an ironic view seeing as my main PC is using a USB ethernet adapter.
I'm also dubious about the reliability of SD cards for something you are using 24/7 and needs to be rock-solid stable. Although I guess with how cheap they are now, keeping a backup card is easy.
My person view overall is a proper router if you plan to run something like OpenWRT, as its easier to update that way. Or an x86 if you plan to use a router OS like pfSense that updates using packages. But that's purely opinion so don't take it as gospel.
