Add IP/Virutal Interface to Eth0(system) or Eth1?

I would like to add an additional IP address to my DA Server. I currently have the system &ns1 tied to the ip addy on eth0 and another ip for ns2 tied to the ip addy on eth1.

Through some reading I find the best way to add an IP to my machine without taking her down and adding a new nic card is to add it via a "virtual interface".
Would I want to add this to the eth0 or the eth1 interface?

Thank you

Whomever told you the best was simply stating his/her own prejudice.

DA uses a completely different method; to see the list of IP#s DA your server is already monitoring:
If you decide to add an IP# manually you need to add it to the interface DA is currently already using; for most of us that's eth0.

Jeff