To me, a single large shared network such as The Things Network is to be preferred over many private networks, as that allows that single network to take full advantage of ADR.
With ADR, nodes may be instructed to lower their transmission power when the network knows they are close to some gateway. Keeping gateways private implies that other nodes need to increase their transmission power to reach gateways that will forward their data. And the higher transmission power will increase the chance of collisions.