The best OS to host on will someday be NixOS, bar none IMO. However, that BEST title will depend heavily on someone sharing a config that leverages the power of NixOS to make it as foolproof and rock-solid as other projects that leverage Nix’s power and reliability.
I’d host an instance if we could would move from the world of Docker being the only game in town toward a more reproducible standard config that uses Nix.