This is a contextual question. If you are talking about a pure visualization tool Tableau is slightly better. Data connectors, modeling and transformation features are available in both. However, factually speaking Power BI is cheaper and offers tighter integration with the Microsoft environment. Since most companies use excel & Microsoft tools they start with Power BI or move towards Power BI for seamless integration with other Microsoft tools (called as Power platform). This makes the job openings grow at a much higher rate on Power BI and Power Platform. Also, Power BI has been leading the Gartner’s magic quadrant in BI for the last few years as the industry leader.