I know all antipsychotics are bad for the elderly. which one is the most effective for elderly agitation?

No concensus: First find cause of agitation.Is the person in pain, has a rash, hypo or hyper=thyroid, uti, anemia, glucose ok? If all non-'psychiatric' causes have been r/o, then behavioral management, for sensory deprivation-check hearing, eye sight, social anxiety etc. If anxious or depressed treat that. If psychotic to the point of being a potential danger to themselves or others then use whatever works.