The first one uses JSON RPC, the second one uses raw websockets.
What I am afraid of using raw websockets is the fact that it doesn't provide the following qualities out of box: memory / scaling / downtime / deployment / resilience / protocol handling / reconnect / metrics / logs / grouping / fanout / security. SignalR provides them but it is kinda limitting the users to using SignalR client which is not available for all languages.