IPSEC VPN or port forward with specific source IP - why is one better?

Been meaning to ask this for a while, so here goes.

I have 2 sites, completely independent of each other, and the HVAC company wants to put in monitoring from one location to another. They require one port to be forwarded for monitoring, and both locations are static IP.

Conversation around this ensued around the ‘proper’ way of doing this, just port forwarding the port to the specific IP only, or setting up IPSEC Tunnel and doing it that way.

From ease - port forward would be quick and easy, but I really wanted to know what the whole story is here to both sides.

Thanks,