MemoryDB: 30% cheaper, 10TB free writes per month and just $0.04/GB (compared to $0.20/GB with the Redis version) after.
And simple, no-downtime upgrades for ElastiCache and MemoryDB.
From my research, MemoryDB is the only actually ACID-compliant Redis-compatible DB engine (using WAL to multi-AZ storage, similar to Aurora) with the same read performance as standard Redis. Standard Redis replication fails Isolation and Durability in failure edge-cases.
AWS really wants you to move away from Redis.
