Ontraport sets the standard and is constantly improving. I've been using it for 7 years now (since before it was Ontraport) for myself and my clients. I'm blown away by the features that keep being added and the fact that I can do so much with the platform without having to use other add-ons.
Support is outstanding and the CEO of the organisation has his finger on the pulse of the community so you know you are being heard when you raise an issue or suggestion.
You can build out a sales funnel end to end without using any other platforms and can even build a website or membership site with it. We mostly use Wordpress which Ontraport integrates with nicely.
We've yet to use the Custom Facebook Audience feature but will certainly make use of that when we dive more deeply into Facebook advertising.
Whether you are just starting out or if you have a well-established business Ontraport will be up to the task. Review collected by and hosted on G2.com.