Attributes  are a key part in making a character and choosing which ones to take along with you when you go into the Labyrinth.  There are 3 attributes to choose from, and each will clash with each other depending on what actions you take.  They also determine to how fast or slow your party rank rises or lowers, and what personalities each character takes on.  Also, certain event scenes where you will be asked if you want to help or ignore someone in need will go by the attributes (i.e. if you choose to help them, anyone with a good or neutral attribute will have their trust level go up and vise versa).  Items with special powers can be used to change one's attribute if you decide to do so.  Changing their attribute does not change their personality (I.E. If you have a Good Human with a personality of 'Jus' and you turn him Evil, his person. will still be 'Jus' and WILL go down if you fight friendly monsters).
Thinks of others before oneself.  Shows mercy to enemies that are friendly.  Actions out of character may change attribute.
Acts accordingly.  Will fight or flee from friendly enemies without changing attributes.
Acts selfishly.  Refuses to show mercy even in front of friendly enemies.  Actions out of character may change attribute.
In my personal opinion, playing a good party pays off (having good/neutral members).  It saves you the trouble of having to fight friendly monsters that could be potentially dangerous.  Also, when you encounter event scenes where you will be asked whether you want to help the person or not, and you choose to do so.. it will make g/n members trust go up faster.

The only advantage to having an evil party (evil/neutral members), is that some of the later equipment can only be used by evil characters.  These weapons are strong, but some of them are also cursed.  Plus, you don't have to worry about running from friendly monsters.