[Patrick_Devine]

It really depends on what you're trying to do, as one is a product and the other is a service.

In terms of jumping in and getting started, AWS can be daunting, but it's not really that difficult to spin up an instance. OpenStack requires you to provision hardware and install a lot of different services, and architect how you want those services to be configured. It's not all that easy to get going (even with Juju, RDO, devstack, etc.). Both have a confusing array of names, so it's not always clear what part is what (ec2 vs nova, iam vs keystone, s3 vs swift/glance, ebs vs cinder, etc.), and not everything is fleshed out yet with OpenStack. I guess you could call it a work in progress. Actually, you could probably say the same with AWS, but it's much more mature.

OpenStack's biggest selling points at this point are that it's ultimately cheaper (in terms of opex) running your own cloud if you're at any kind of scale, but AWS saves you a lot up front (in terms of capex). OpenStack doesn't lock you in to a particular vendor and you can swap out parts like the hypervisor if you decide you want ESX or Xen over KVM. Unless you're using spot instances on EC2, AWS can be a lot more expensive (it would take only a few months to pay off a server if you're paying On Demand prices).