Look, I'm biased because I'm the CTO of Aerospike, but we do give a free and unlimited open source edition, and our enterprise customers save a _TON_ of money compared to Cassandra, because we're not bottlenecked on CPU, and we use less power-hungry DRAM and more NAND Flash. In several recent customers, we save them literally a million dollars a year.

PayPal has a ton of Aerospike in production now, and they're very happy about it.

Thus I can claim we are simply better, and we are doing fundamental systems engineering to make it so. If you're a C and systems engineer who wants to solve real high performance problems and is sick of "just make it scale don't make it efficient", our offices are in Mt View and we're always hiring, drop me a line...