We have 2 options to run garbase collection
1) runDataStoreGarbageCollection(java.lang.Boolean delete) at /system/console/jmx/com.adobe.granite%3Atype%3DRepository
2) startRevisionGC() at /system/console/jmx/org.apache.jackrabbit.oak%3Aid%3D15%2Cname%3D"repository+manager"%2Ctype%3D"RepositoryManagement"
Which one is correct and when to run what? What is the difference between both?
Thank you in advance.
runDataStoreGarbageCollection - This will trigger the data store garbage collection.
startRevisionGC() - This will trigger oak revision cleanup(Compaction) which should not be run on AEM version 6.2 and below.
To answer your question, you need to run "runDataStoreGarbageCollection" to run datastore Garbage collection.
You can find other ways of running DSGC at 
That being said, AEM 6.1 is out of support, please upgrade to the latest version of AEM.
 Data Store Garbage Collection