I will be working on a VR multiplayer game for a one time event and I’ve been evaluating Mirror, Netcode for Gameobjects and FishNet, all three seem pretty similar and simple to use, but since this is going to be for a one time event what’s more important is that it has to be super reliable and it has to work smoothly with rigidbodies since players are going to be grabbing and throwing stuff.
What is your experience working with any of those libraries?
They all work fine. Your implementation will have greater impact than the library. FishNet seems to have the greatest statistical value, but the others also work fine.
I use Fishnet myself and the LAN setup is super simple. It’s a network discovery type setup.
Hop on he Discord if you need help.
Good on you for trying out all the assets btw! There are a few other assets out there so don’t forget to take a look at those if you find these lacking.
They are all “reliable”. Not sure how something can be more reliable than reliable unless you’re asking for something concrete that can be measured and actually represents a measurement of reliability (number of bugs isn’t because bugs might simply not have been reported as much or not listed publicly). But I digress … 
Fish-Net likely has an advantage here because it supports client-side prediction of physics objects if I recall correctly. You’ve seen the feature comparison chart ?