As a Best Practice Which of the Following Should Be

As a best practice which of the following should be used to ingest data on clustered indexers?

A) Monitoring (via a process) , collecting data (modular inputs) from remote systems/applications
B) Modular inputs, HTTP Event Collector (HEC) , inputs.conf monitor stanza Modular inputs, HTTP Event Collector (HEC) , inputs.conf monitor stanza
C) Actively listening on ports, monitoring (via a process) , collecting data from remote systems/applications
D) splunktcp , splunktcp-ssl , HTTP Event Collector (HEC) splunktcp , splunktcp-ssl , HTTP Event Collector (HEC)