I recently needed to stand up a DB2 server and was going to reach for my trusty rackspace account, but didn't feel like setting up DB2 for an experiment that would only last a few hours.
Instead I turned to amazon. It turns out that amazon has preconfigured images for ubuntu/db2 that you can spin up almost instantaneously. In addition, their security model is a little more robust. Key things they do right from a security perspective (compared to rackspace).
#1 They never send you a root password (via email or otherwise). You must generate a public/private key pair and download the key via https. Assuming you keep your secret key secure, there is minimal (if any) opportunity for someone to steal this key. Even if they hack your amazon account, I'm not sure they could get to your server immediately, even though they certainly could shut it down.
#2 By default you are behind a firewall so that only a minimal set of tcp ports are even open. You need to actually take action before they will allow ssh access to the server.
#3 The root account is locked and cannot log in from a remote location. You MUST log in via a "normal" user (ubuntu on this image) and then switch to root.
All told, it seems like EC2 has got a more secure default setup than Rackspace. I haven't yet compared pricing or service levels on the two, but purely from a security perspective, RackspaceAWS certainly has got it's stuff together.