Since Legacy is basically trying to revive old (EVEN YEARS OLD), dead threads I'll just contribute what I think.
Most Zombie players have heard about Z9's server. Its almost always full, and when it's not it has at least 20+ players.
BUT what makes it so popular?
BEST REASON: TEAM SWITCHING
Every map, the teams change. I don't mean the humans get changed to the red team, I mean the blue team becomes zombies, so the blue team gets knifes and the red team gets guns, then vice versa the next map.
I like this idea better than the idea posted by 1up members and some other contributors where the players get switched sides halfway during the map, after or during round 5 (out of 10).
What I'm proposing is that if a 2nd Zombie TS server were to be made, this would be a good option - to give it difference to the current TS server. Also, as Wargasm stated, different weapons on blues would be a nice change for the 2nd server. Although, if a standard auto were to replace the negev, please don't make it too underpowered (like what infinity team has basically done, they're practically useless in the hands of an unexperienced or as I'd call it, "unworthy" player.