EVC needs to be set to the CPU with the lowest feature set, which - assuming you want to live migrate VMs between all of your clusters - would be the one for the E5-2630 v4 CPUs, i.e. "Broadwell".
Please note that setting an EVC mode requires that a.) the host's CPU supports that mode, and b.) no VM is currently running with a higher mode (with CPU features that are not provided by the EVC mode).
André