It depends on how you define "easy", because there are multiple factors to consider, including but not limited to; pain level, accessibility, success rate, and so on. Overall, I would argue that, regrettably, no method is flat-out easy. Those methods which I personally consider the easiest (CO/He/N inhalation, certain drugs e.g. nembutal, opioid overdose), whilst being easy in terms of entailing little to no pain, are still fraught with other challenges, because for example one must know how to prepare/administer the drugs, and acquiring the necessary materials is difficult, mainly due to legality. Ultimately though the difficulty is subjective; what I personally find difficult, another may find effortless to achieve.