Stackify Retrace is a simple SaaS application monitoring solution that integrates a number of essential features such as APM, logs, metrics, and more. It gathers a large quantity of information about the health and performance of your application.
New Relic and Atatus both ensure application performance through operational data monitoring, application monitoring, and infrastructure monitoring features. Since most companies offer those monitoring features, New Relic and Atatus are the best in the business.
If you want an APM that you can get all the features one would need in understanding performance monitoring of your apps. Read about all the NewRelic alternatives here.