IMO, I categorize them as follows:
Hard, Easy, Long, Expensive and Grindy.
Easy:
Titles that can be gained within week.. e.g. Protectors, Cartographers.
Hard:
Titles that need serious experience in gaming. e.g. Master of North (without 600's in dungeons), Guardians.
Long:
Titles that takes usually from months to years. e.g. Player, PvP, Allegiance with AB.
Expensive:
Titles that need a lot of cash. e.g. Treasure, Zaishen, Drunkard/Sweets.
Grindy:
That need a repetitive doing of things. e.g. EoTN titles, SS, LB, VQ, "Expensive" titles farming (to get cash).
I summarize, that I agree with Easy and Hard.
Rest are for non-lifers or those who don't have other games or bored or very willing or play for long time and don't get tired.