The verdict
If your data is scattered across billing, CRM and product tools and there is no single place where it joins, I'd pick BigQuery first. Without a clean store, a dashboard tool only shows you the mess faster.
If the data already sits in a database or spreadsheets and the team needs governed dashboards and self-serve exploration, pick Tableau. It suits data, finance and operations teams with someone to own the model.
At scale, many teams use both, with BigQuery as the store and Tableau on top. For a small B2B team that only needs a few dashboards, neither is the right first step. A lighter tool such as Looker Studio or Databox gets you there with less setup.