The CRM market is saturated with many great CRM tools that can radically improve any business, so this question is subjective. It also depends on what industry you are in because even if they don’t call it “CRM”, every industry uses some type of system to track clients and leads.
For example, many colleges in the higher education industry use CampusVue. In the law industry, many firms have used Needles for decades. Every CRM has its pros and cons, but my favorite is Salesforce. HubSpot is a close second. I am certified in Salesforce and have years of experience with it, so I am definitely biased. They have consistently made Gardner’s Magic Quadrant for CRMs a leader in the industry, and that is a very high honor for a SaaS company.