The better system would be to eliminate the ability for people to not answer. Right now, no answer means no, whereas in the ideal system, answering would be mandatory, eliminating the need for opting in or out.
Opting out is a presumption of consent. For something as vital as vital organs (heh) there must be freely given consent, not simply presumed consent. If presumed consent is okay for harvesting organs, why is presumed consent so uncommon in other aspects of life?