The best caching strategy for populating real-time dashboards using Amazon ElastiCache is a write-through caching strategy. In this strategy, when new data is written to the database, it is also written to the cache simultaneously. This ensures that the most current data is always available in the cache for the real-time dashboards to access, which reduces the latency of the data retrieval. Additionally, using a write-through cache ensures that data consistency is maintained between the database and the cache, as any changes to the data are written to both locations at the same time.