Generally consider what kind of security you wish to have.
POW may have 51% mining concentration, yet this actor can still be diluted anytime as new miners join the global hash rate. If people transact with higher fees, this will provide incentive for more new hash rate to join, balancing the power of the previously 51% miner. Because POW relies on external resources (external to the System of Bitcoin), it can always balance miner power.
POS suffers from the problem that a 51% miner can not be unseated without his cooperation. This miner now has the power to censor all transactions if it chooses to. Since the mining ability is proportional to stake, and the stake is internal to the system (no additional stake can be acquired externally), the system simply has no way to balance the power of a 51% miner.
Other consensus algorithms may be designed to deliver proofs in different forms (memory space, hard drive space, other resources), but always consider if these are external or internal to System. That is the key difference in system security.