If you have a very dynamic environment (a.k.a. virtualisation, cloud, etc) usually you have to go one level furter and integrate your provisioning tools with the monitoring (and backups) system.
I've never used sensu, but I've write my own monitoring and reporting tools many times. I can recommend you to try to get that skill, learn howto script a protocol and report, etc... probably you will need it to adapt your monitoring tool, whatever you choose.
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Nagios is great if you manage bare metal.
If you have a very dynamic environment (a.k.a. virtualisation, cloud, etc) usually you have to go one level furter and integrate your provisioning tools with the monitoring (and backups) system.
I've never used sensu, but I've write my own monitoring and reporting tools many times. I can recommend you to try to get that skill, learn howto script a protocol and report, etc... probably you will need it to adapt your monitoring tool, whatever you choose.
Also, as you ask for experiences:
In my current and previous job, nagios, with nrpe.
Before that, in a shop I did have only Debian servers, I did write my own dashboard.
The reason has been always pragmatism.