Windows Server 2019 Datacenter Key Global is usually used for virtualization as it allows you to put a lot of virtual machines (VMs) on a single physical host.  Datacenter, the same as Standard, needs CALs, but it allows for an unlimited number of virtual machines to be executed.

However, the cost of a Datacenter license is approximatively 7 times the cost of a Standard license, so if you are running less 14 VMs on a physical server it is generally less costly to get just the Standard.

Datacenter
Highly virtualized datacenters and cloud environments, Core-based, Windows Server CAL, Pricing Open NL ERP: 6155 USD 

Standard
Physical or minimally virtualized environments, Core-based, Windows Server CAL, Pricing Open NL ERP: 972 USD

Essentials
Small businesses with up to 25 users and 50 devices, Specialty servers (server license), No CAL required, Pricing Open NL ERP: 501 USD