You need to ask yourself, what is your main use case? More often than not, if your use case is a web service serving up files over HTTP then Amazon is more competitive. I would say bandwidth would be the greater consideration in most cases for web services.
All of their comparison calculations (http://www.rackspace.com/cloud/cloud_hosting_products/files/...) also include "AWS Gold Support" (which costs an extra $400+/month).
I know you weren't saying the contrary, but still I wanted to point it out.
ssl.SSLError: The read operation timed out
I'm not the only one:
It's not that bad since I just retry it but it's one of the things that makes me wonder what is going on at Rackspace.
The object versioning system seems interesting if you haven't rolled your own yet, though I wonder how relying on it might affect your ability to migrate to Amazon.
I haven't looked at the RS versioning offering, but I can't imagine it being any different in terms of features of the amazon one.
You can leverage these with Rackspace Cloud Files.
 Arq: http://www.haystacksoftware.com/arq/
There is a very easy to use command line interace, and also a GUI (which I have not tried).
It doesn't even have to be something as 'cloudy' as rackspace, support for something like webdav as an ARQ backend would also be nice.
That being said, I have actually no idea about the codebase and user base, so this could be a completely wrong assumption :)
Personally, my biggest 'problem' with Arq at the moment is, that the iPhone client works, but I'm missing stupid small things like thumbnail previews for uploaded images.
Basically I think we are paying for all of their support people and infrastructure and also a healthy profit.
If I have an instance with 8x CPU cores they can timeshare CPU time between multiple customers on that physical server, since it's unlikely that all instances will use 100% CPU 100% of the time.
However, if I have a server running memcached and a 30GB cache, they can't also cell that RAM to another customer. This limits the amount they can oversell server resources, thus they charge more for it.