These advantages Rackspace Cloud has over Amazon EC2 (AWS) have made me switch from EC2 to RSC and never look back since:
1) RSC’s storage is directly attached and persistent. This means fast I/O, and that you don’t (necessarily) lose your data in the event of a crash or reboot. To get persistence with EC2 you have to pay for one or more EBS volumes, and they’re still not directly attached.
2) Where Amazon gives you ceilings, RSC gives you floors. EC2 says “This is how much CPU you get,” while RSC says “You’ll get at least this much CPU, and you can burst if there’s more available.”
3) A much better scaling model. If I need to scale on EC2, I have to launch additional instances (which you can do with stored AMI’s). At RSC, I can point to a running instance and click a button to say “Make this server bigger” (or smaller if you need to scale down). A few minutes later, it’s all done. I have the option of adding additional instances, too, of course, but it’s not my only relief.
4) Support! Amazon has pay-per-incident support. I’ve never used it, and can’t speak to its quality. If you’re using Cloud Sites, Rackspace sysadmins manage your instance(s) for you. If you’re using Cloud Servers, you manage your own instance(s) but still get their support* which really is as good as they say it is.
5) Hybrid deployments. I’m not using this, but for larger deployments you can mix-and-match VPS instances and dedicated hardware, and they’ll work pretty seamlessly together. Amazon doesn’t offer this at all.
6) DNS and reverse DNS. DNS services are common (though EC2 doesn’t offer them), but reverse DNS is unheard of. I love that if you look up my host’s IP you get back my hostname instead of some convoluted hostname set by my hosting provider.
There are a few services Amazon offers that RSC doesn’t yet, but I really haven’t missed any of them (your needs may differ). RSC gives me everything I need to run the stuff I run, the price is unbeatable, and managing all of it is simple as can be.
*RSC currently offers free support for all Cloud Servers customers, but in the future it will be available only to those who spend $100/month or more – still a much better deal than EC2’s support model, and it’s still Rackspace support, which is awesome.