Site24x7

I've been with Site24x7 since early days and the team keep adding functionality and more granular and complex ways to test my essential services. Service is always on and both custom and provided distributed pollers are rock solid--if there's an alert I can be sure it's not a false negative.They also provide plenty of statistics and pre-alert diagnosis so things like regional outages or problems with a registrar are obvious from the outset.Plenty of ways to notify, including integrations with 3rd party solutions such as PagerDuty and xMatters for scheduling team coverage and response.

Initially the service was limited in some ways but the team was very responsive to feedback and quickly upped their game.I think the only thing I'd like to change now is automatic ssl cert issue detection/warning of impending expiration for all https monitors.

Alerts can easily be customized to be as noisy as you want or not at all and everywhere in-between. A lot of options such as SMS/Email/etc for alerting as well fantastic bonus features such as a NOC view makes this product stand out from the rest.

The recorded steps feature overall is great but I would like the ability more easily edit the steps as right now it's a little too complex to modify the existing recording.

It supports a large variety of products and services built-in. The agents are fairly easy to install/setup. There is a decent amount of documentation available. Custom monitor plugins are very easy to create.

Doesn't support all the latest languages and platforms. They are a little slow at adding the latest and greatest. Their agents seem a little hacked together are are not as resource efficient as others. You have to manually upgrade/downgrade your plan as your usage changes. Most/All portions won't automatically scale and don't even have an option for them to, so things will stop working as you grow and you'll be over-billed as you shrink. Their PHP APM flat out doesn't work. Things will stop working and give you no indication as to why. You must reach out to support, wait a day or so, they will ask for logs, wait a day or so, provide some feedback. Then a week or month later you'll have to do it all over again.