What bouke said is not correct.
Line - License vCenter Server - This will show the licensed vCenter Server chosen by vcops as master one.
Say if you have registered 1st VCenter Server - 100 vm capacity
Now if u have registered 2nd vCenter Server - 1000 vm capacity.
In this case, 2nd vCenter Server will be shown in License vCenter Server.
So this is the logic - Highest License SKU, if tis same, then Highest Entitlement will treated as Master one.