Opnsense or OpenWRT in my case?

the situation is this: I need to turn a VM into a router .
The node represented by the VM will sit between a gateway and a virtual bridge for the local LAN. so basically a 2 ports router, 1 WAN and 1 LAN.

The gateway provided by the ISP has a bunch of static public IPs and RJ45 ports, but given the fact that is a GW once I connect anything to it I'm on the internet without any firewall / protection.

I don't think that throughput will be an issue here, the ISP provides ~300Mb/s of bandwidth in download on a good day and a few Mb/s in upload, and all the RJ45 ports on the host machine running the VMs are gigabit.

My main concern right now is stability and the performance of the NAT and the firewall.

The only task for this VM will be the translation from WAN to LAN and viceversa ( no samba/cifs, no DNS, no DHCP, no nothing else ): do you have any input that could help me pick one over the other ?