To be fair, it seems Memorystore instance is not the same gb-for-gb as Elasticache, since Memorystore gives you extra memory overhead, and on aws you have to manage it yourself. Memorystore also has free network egress/ingress. There is also a RedisLabs offering on Google Cloud with integrated billing.
if you run Redis you need at least 25% of extra RAM on top the instance memorysize if you want to avoid a lot of nasty OOM scenarios. Memorystore gives this memory by default and in aws you need to tweak the reserved-memory. https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/...
Disclaimer: I work at Google Cloud.