The real question is not if a more efficient system is possible.
The real question is:
What is the most secure system possible ?
So far I have seen two systems:
1. Majority of vote. (suggested alternative coin system).
2. Majority of computational power (bitcoin).
To make it a little more meta (and understand Bitcoin better) I would abstract it this way.
All consensus systems are based on votes. So your two examples are
1. Majority of vote (1 person = 1 vote)
2. Majority of vote (1 hash = 1 vote)
also you could include
3. Majority of vote (1 coin = 1 vote)
4. Majority of vote (1 transaction log of x transactions = 1 vote) <- voted weighted by age of entity (older more active entities are given more weight)
5. Majority of vote (hybrid system included 2+ of the above x OR y )
6. Majority of vote (layered system which requires 2+ of the above x AND y)