Each player has a TNManager.ping of their own, and it's a local value representing the time it takes for a packet to travel from the player to the server and back. This value is only on the client-side right now, so you would have to have the host ask everyone in the channel what their current ping is, then pick the best one to be the host.
Keep in mind though, the ping can spike, and often varies greatly. Choosing a host on player join may not be the best option. Doing checks periodically and averaging out the result is a better alternative.