This is comprised of a number of elements as I am sure you already know - transparency of the public code with strong third party analysis ... ethical hacking to examine the veracity ... hackathons  ... without that I would hesitate to invest or use ... a lot of vaporware ... also the mining technique ... in our view PoW is best for security but creates scalability and cost issues ... PoS is the logical alternative [see ETH fork] ... safer if the network is at critical mass and less so with nascent chains ... control over the chain is the key ... next issue is control of the cryptocurrency or cryptoasset ... take a look at the abacas exchange as the dev is driven by the concerns that you have - building a better mousetrap