Assuming you must choose the host out of a fixed group of players that will all play the same game (not a big pool of players that needs grouping into games such that everyone has good RTT with their host)
1.Connect all the players together
2.Measure round trip times, possibly bandwidth and other data
3.Use some algorithm to sort everyone based on how good hosts they are. Combine the above RTT etc. data along with player data you have recorded earlier (like how often they disconnect mid game, frequent problems with connection...)
4.Pick the best one
For sorting you might want to measure, in order of importance:
-Connectivity - can all players connect to the host
-Bandwidth (can the player handle the required traffic at all)
-RTT (best playing experience for all players. Minimum RTT, minimum variance in RTT)
-Quality of connection (occasional slowdowns, quitting mid game, corrupted/lost packets)
So first make sure he can act as a host, then look into the quality of the connection.
The lack of awesome free resource gathering building sandbox games capable of running an user made 8 bit computer in the world disturbs me.