Better to do this on NEO instead. Their tech is better than ETH in every way; it can handle up to 10.000 transactions per second (whereas ETH can handle ~15) and it supports almost all mainstream coding languages. What's more, transactions are free.
You can totally build something Cryptokitties with NEO -- the only difference is that because there isn't a standard, there isn't a third-party marketplace for these assets. (i.e., there's nothing inherent about NEO that prevents something like Cryptokitties from being built.)
Time will tell which one is safe. If the rewards are high enough, someone powerful/knowledgeable will inevitably try and break or cheat the system.
† Some people like to make a distinction between "distributed" and "decentralized". For me the former is part of the latter.