Who was more psychotic
Napier
Ledger’s Joker
Arthur
Remember Napier was fairly young when he killed the Waynes
We know very little about Jack and Ledger's lives, but they both display SOME symptoms of Psychosis in their movies. Arthur on the other hand, we know very well, and he just about has all the symptoms associated with psychotic behavior. I pick Arthur, simply because we get to see his life from his POV and we know more about him.
Psychotic disorder symptoms.
Behavioral: disorganized behavior, aggression, agitation, hostility, hyperactivity, hypervigilance, nonsense word repetition, repetitive movements, restlessness, self-harm, social isolation, lack of restraint, or persistent repetition of words or actions
Cognitive: thought disorder, confusion, belief that an ordinary event has special and personal meaning, belief that thoughts aren't one's own, disorientation, memory loss, racing thoughts, slowness in activity, thoughts of suicide, unwanted thoughts, difficulty thinking and understanding, or false belief of superiority
Mood: anger, anxiety, apathy, excitement, feeling detached from self, general discontent, limited range of emotions, loneliness, or nervousness
Psychological: fear, hearing voices, depression, manic episode, paranoia, persecutory delusion, religious delusion, or visual hallucinations
Speech: deficiency of speech, excessive wordiness, incoherent speech, or rapid and frenzied speaking
Also common: nightmares or tactile hallucination
In short, Arthur displays just about everything on that list.