Which is better for sleep onset problems? xyprexa or saphris (asenapine)?

Neither one: Both medications are antipsychotics prescribed for bipolar disorder or schizophrenia. They can have a role in very severe depression that doesn't respond to other therapy, but neither is prescribed for insomnia. That being said, either medication can make you drowsy, but perhaps counterintuitively they both also commonly cause insomnia. I would not recommend either of these for sleep.