Malpractice: Compare and contrast defenses

In medical malpractice cases, some of the most commonly claimed defenses include claiming the case is outside of the statute of limitations, the patient was negligent (comparative negligence), assumption of the risk, Exculpatory contracts, Release, Good Samaritan Statutes, Worker’s Compensation, or even Governmental immunity. Which of these do you believe is the most difficult to prove and which do you believe is the easiest?  Provide rationales to support each of your claims.  Respond in 200 - 300 words max and Include at least 2 references in APA format.