They are all pretty easy these days. Keep in mind some of the strategies may have changed over time from what the videos say so be prepared to adapt on the fly.

Titan is by far the most difficult of all of them.

It's very likely that the King Moggle Mog wipes weren't your fault. I'm presuming everyone died to a big attack in the 2nd phase (this is what usually happens). Mog will do the Memento Moogle attack when his HP reaches a certain threshold (around 60% iirc) and that attack will one shot everyone if not enough small moogles are dead before it goes off (I think you need no more than 3 alive). More than likely your tank or the DPS were pushing his HP too low before enough moogles had been killed and you can't heal through a one shot.