Snipers Tourney recommended.

about the zombie tournament suggestion,
I think it really sucks to play the zombie tournament on zm_novum.
Easy to win but not enjoyable...

haha, yeah, zm_atix-helicopter map is more challenging one because sometimes at the 30 seconds before the big explosion, humans are in the heli and zombie can still jump from the roof to the heli and make a lot of infection  :o

atix_helicopter is ok, but you should use atix_helicopter_mini, where the secret door leads you to the chopper stop(where players usually camp and wait for chopper). The normal atix helicopter will lead you to the room with secret button.
If the button is pressed, then from the chopper you can jump out to a street light, then enter the wtf room, get out and get 1000 kills . But I think in atix helicopter mini you can still get into the secret button room from outside. However, you can get 1000 kills there and atix helicopter is not a real zombie map. It is a half-zombie and half-ze map.
I recommend one of the new maps of one of lila panic maps.