APM products are something that needs to be well-tailored to your specific needs and environment. for the project i'm currently working on, we chose new relic after a bakeoff with another vendor. both products were great, but new relic came up on top and we've been very happy with the insights it provides.
This review assumes one is familiar with APM and will not cover the basic benefits of New Relic as an APM product.
New Relic was very easy to deploy and had minimal impact on our environments. Visibility was near-total out of the box and support was extremely helpful in adding the missing instrumentation into the product.
New Relic supports a good mix of environments which is important to us as we work with several languages.
Support for background tasks is also an important feature for us which is usually not as well-covered in other products.