We use Hubspot CRM across our company for managing the entire spectrum of our contacts (leads, clients, and our certified coaches). Presently, we sync Hubspot CRM with another marketing automation tool to deploy email nurture campaigns and the email components of our programs for clients, but we will probably bring that all under one roof with Hubspot before too long.
Hubspot CRM does a great job of balancing flexibility (we can structure it how we want and create unlimited custom properties to support that setup) with ease of use (it doesn't take one or more dedicated and trained staff to build our setup and maintain it for us). Since we're a small and growing company, we've been able to easily adapt Hubspot CRM to our needs as our company has changed from a strategic and personnel standpoint.
Hubspot CRM is also the most integration-friendly tool our stack. Since it's so popular, most marketing and product software platforms integrate with it one way or another. It's made it very easy for us to plug in our other tools and build some fun automation, both client-facing and backstage.