EMT, but if you're a chiropractor why go for RN if you don't mind me asking. (I don't know the difference in school etc, but aren't you a doctor?)
CNA's bascially help with activities of daily living. So you'd be trained in transfers, feeding, dressing, and vitals.
EMT- you'd be trained in handling the basics of trauma and emergency situations. I'd think that experience would make it easier to land an ER position, where CNA might make it easier to work med/surg or NH.