What is the best perk in black ops 2 zombies?

Ascension has 2 new perks both for 2,000 points PhD Flopper and Stamin-Up see excert form related link

PhD Flopper; located outside near the Lunar Lander launch pad that has the Fragmentation Grenades. This perk makes the player drop a small 'nuke' when diving to prone (almost anything above flat ground). The 'nuke' kills all nearby Zombies. In addition, the player absorbs any explosive damage done to the player, including Ray Gun's splash damage, fragmentation grenades and Matryoshka Dolls.

Stamin-Up; located near the AK-74u, towards another Lunar Lander launch pad. This perk gives the player increased movement speed and sprint duration, similar to Marathon or Lightweight. Since Ascension is a rather large map, it is more useful than one might think, especially during Space Monkey rounds where a player may have to get to a Perk-a-Cola machine that is being attacked.