I voted for Poison Heal.
As stated about 100 times already, custom abilities should be avoided unless a current ability does not help the concept. Therefor, with Posion Heal, Guts, Marvel Scale, Magic Guard, Synchronise, Quick Feet, and all of the 'X is immune to Y status' abilities, I think we can say that AMC is not needed.
Guts, while good, I feel will be broken on a CAP with a Base speed that seems like it will top 100, and a Base Attack that seems like it will top 110. Machamp and Heracross (The two OU Guts users), both have massive attack, but both are hampered by poor speed. Same goes for almost all guts users. There's a reason why a fast, already powerful pokemon hasn't been given Guts already.
This left me with Poison Heal. Which, is a good ability. Near Immunity to status, full immunity if you get a free-switch in on one of CAP9's immunities (Thunder Wave, Electric Attacks, Psychic Attacks, or, in this case, Toxic). In addittion, it cures this otherwise Toxic Spikes weak CAP of that weakness. Considering it seems like it's already been decided that this CAP will have Rapid Spin (Another reason for the Dark Type, and just look at the Art thread. More than enough pics showing the concept Rapid Spinning), Toxic Spikes not dealing damage, but healing instead sounds like a good idea. Let's all remember, if CAP9 has a Toxic Orb, it's blocked from ALL status after the turn that it's switched in. Burns, Freeze, Sleep, Paralysis from Body Slam and Stun Spore/Glare, and Poision. So those of you saying it stops 1 kind of status, are speaking nonsence.
Remember, with Poision Heal, on a bulky pokemon, (Unlike Breloom), you can switch in. Predict a Toxic from Blissey? CAP9. Toxic Spikes are up from Roserade? CAP9. And you can still slap Leftovers/Life Orb ect on it too, so you get either insane healing, that Stallrein would be jeleous of, or Life Orb recoil healed right off.
Anyone besides me noticed that, despite the lack of in-thread posts supporting Auto Magic Coat, it's winning?