I do not know about aerospike, have never run their software but Scylla are the champions in what they are doing. Having said that, Scylla provide full durability guarantees, that means they need to touch a disk upon each write or update. Disk I/O is relativle expensive in the cloud and requires either large instances or special storage optimized family types like i3 etc.

Long story short, I do think Dragonfly is the fastest in-memory database in terms of throughput and latency today. We will see if we manage to stay this way when we extend our capabilities with SSD tiering.