Which person would be more volatile: one with a sadistic personality disorder or a sociopath (antisocial personality disorder)?

Volatility: Sadistic personality, as a specified disorder had a short run. It is not in the current manual and not likely in the dsm v. Both psychopathy and sadism stem, in part, from preoccupations with self serving behaviors & low empathy/reciprocity. Volatility is associated with drug abuse, mania, impulsivity and in response to threats to something valued. Forced to choose - antisocial > sadistic.

Sociopath: Either of these can be emotionally volatile, or hardly at all. There is no one-size-fits-all distinction. To illustrate antisocial personality disorder, white collar criminals like Bernie Madoff are typically not violent at all, whereas serial killers like Ted Bundy are incredibly violent and volatile.