What is the best way to measure speed and performance on Windows 2008 server? There are free trials on ElasticHosts, Rackspace and few others, so I would to take that opportunity and test them before I commit.
Simulate your workload, in as close to production style as possible. For example, performance of the ephemeral (local instance) disk on Amazon EC2 tends to be much better (or at least, much more consistent) than EBS volumes. If you just run a benchmark on a default instance without using EBS root — which you would probably want in production — you might not notice that.
Also, performance will vary over time, depending on the workload of other guests on the same host as your instances.
The single best thing you can do is - whatever you actually want to do. If you can't do that and have to run benchmark software, consider a variety of representative tests (is your application CPU heavy? Network heavy?) and repeat them over a period of time.