The discrepancy you’re seeing between Pavlos Daskalakis (Παύλος Δασκαλάκης)’s answer to How do I phonetically write my name in Greek? and Goru Yamato’s answer to How do I phonetically write my name in Greek? are two:
- Where you accent Cotera on, as Goru said;
- Whether you want to assimilate Hristo linguistically and make it declinable (Χρήστος), or keep it indeclinable (Χρήστο, or indeed just phonetically spelled Χρίστο). That basically depends on whether you want to assimilate into the society or not. If you’re going to be in conversation with Greeks, assimilating is a gesture that will be appreciated; if this is just a one off, or if you are unlikely to be chatting to them in Greek, it’s unnecessary.