Datadog was down so often when I had to use it. It felt so unreliable. We used to monitor hosts and it got to the point where checking if datadog was down was part of troubleshooting..
As far as Datadog goes, it's the most team friendly dashboard system we've used. We had a specialty monitoring system for one application stack previously, and no one made custom dashboards there or even just looked at the data. Now we've got custom dashboards out the nose and we're gradually consolidating to a "best of" dashboard for each service.
Are you affiliated with Wavefront?
(I've learned not to trust numbers that seem too good to be true unless they're contractually obligated.)
Wavefront doesn't publish pricing, but if we take Librato's pricing as a general indication you're talking several million dollars a month.
I used it up until two months ago when I left that job. There was 2000~ servers monitored I think.