Relational data = Dataverse/Dynamics 365 Sales, or SQL
Unstructured data = SharePoint
Also, think of future extension and expansion. Suspect you are after more of a CRM than SharePoint - Dataverse will give you Contacts and Accounts (Organisations) out of the box plus a lot more, Dynamics 365 for Sales will give you a whole lot more from a sales point of view.
As per Eric I am a little bit biased as the CRM/Dynamics 365 is my background - but you need to use the tool that works best with the type of data that you will be handling.