Which of the following is the most efficient search?

 Option A is the most efficient search because it uses the tstats command, which is a fast and scalable way to search indexed fields in the _internal index. The tstats command does not need to retrieve the raw events from the index, but instead uses the tsidx files that store the metadata and summary information about the events. The tstats command also supports distributed search and can run on multiple indexers in parallel. Option B is less efficient because it uses the stats command, which requires retrieving the raw events from the index and performing calculations on them. Option C is less efficient because it does not specify the index or source type, which means it will search all the data on the instance. Option D is less efficient because it uses the search command, which is redundant and slows down the search performance. References:

Types of searches - Splunk Documentation

Quick tips for optimization - Splunk Documentation

Solved: best tips for speeding up searches? - Splunk Community