This depends on your current infrastructure, your expected growth over the next few years and obviously your software stack. In my experience, unless you are doing something with extreme latency or scaling requirements, AWS is likely cheaper in TCO, at least in the beginning where your fleet is less than a few hundreds machines. Also note that AWS is not just EC2. Other services like S3 or Dynamo can be life savers. The downside of AWS is that you can become over reliant of it.