Assuming that you are asking for the vCenter Server license edition, then yes, it's the vCenter Server Standard edition. Foundation can only be used with up to 4 ESXi hosts.
Please remember that in addition to vCenter Server, you will also have to get the required ESXi (CPU) licenses. The ESXi license edition (Standard, Enterprise Plus, ...) depends on the features you want/need.
Like the Essentials Kit, you will need a license for vCenter Server, and licenses for the ESXi hosts (CPU sockets).
Assuming each of your 6 ESXi hosts has 2 CPU sockets, you'll need 1 instance of vCenter Server Standard, and 12 CPU licenses for your ESXi hosts.
VMware offers "Acceleration Kits" which consists of 1 instance for vCenter Server Standard, and 6 CPU licenses (available as Standard, or Enterprise Plus), These Acceleration Kits are meant as a "Starter" packs, that can be purchased once per site at a lower price than purchasing all components separately. If you decide to go for this, you'll just need to get additional CPU licenses to cover all of your hosts.