hi not sure which ability is bast
ev are in half in attack and defense / sp def max out / and speed
move set is Confide / Zen Headbutt / Milk Drink / Body Slam
held item is rocky helmet
You should go for scrappy because it will have an offence towards ghost types with body slam.
I think thick fat would be a much better option.
You have zen headbut that can hit ghost types in a pinch and you would be better off facing a ghost type with a proper type advantage "dark/ghost".
Miltank is a tank type Pokemon (high hp, high defence). Give it the ability that would benefit a tank! like halving fire and ice damage with Thick Fat.