If you have dry backend, the Zone Classic. If the lanes are oilier and tend to be spotty, the Impulse Zone (more grip).
The AI might be close to the Vertigo, maybe a bit longer, the Nemesis is a cheaper option, good all around ball, but I'd set for the Impulse Zone because the asymmetric core can be fine-tuned to your game for additional effect.
Maybe a Monster Bruiser could also be a good in-between ball. Watch out for close-outs, since it might be discontinued this summer.
--------------------
DizzyFugu --- Reporting from Germany
"All that we see or seem, is but a dream within a dream..." - Edgar Allen Poe