here is some of tips :
I loved the idea of a reflect spell in Wonderland Online, but as it's only useful against 1 target magic attack, it's so easily circumvented. Even in a single player PVP, a mage opponent could still use as an AoE attack, and thus the Warrior's Holy Shield would not protect him.
Important to note also that the Water's Goddess Skill Shrink can't be coupled with the Wit's Curse for a combined effect. Although, as the first halves the Att/Def/Matt and MDef of the target, and the Wit's Cuss only doubles the damage, wouldn't Shrink me more useful? In halving the targets Def and MDef, you've effectively doubled the damage, so that ties it with Cuss. But Shrink also seriously hampers the targets ability to do damage in turn.
These are all very important points to consider for a team to work together effectively. I think, also your character's element would be an important thing to consider before choosing your class. After all, there's little point in choosing the Wit for a Water. Shink and Curse are effectively of the same usefulness, so why pass up the opportiunity to have a Priest, or Seer?
To a lesser extent, the same applies to Knight. A water (or even an Earth) Knight would limit their own support capabilities after the Spirit has been cast. Of course the same applies if said Water (or Earth) are in a team with a Knight.
But let's instead look at at the classes themselves:
Knight (Spirit) is a multi-target protection, that will probably hit first, so long as the knight is fast enough. This means, the Knight class is best suited to high agility characters (such as the Wind physical) although applicable to all types if you keep your speed up.
Warrior (Reflect) is a single target protection, with several flaws, including not only it's inability to reflect AoE, but the likelyhood of it being cancelled by your own teams Support spells.
Killer (Murder) is a single target attack non-elemental attack spell, that'd doubly effect on trapped targets. Basically, it has no weakesses in the skill, other than the weaknesses of the character using it.
Wit (Cuss) is a single target debuff, which only weakness is that it's non-stackable with the Water's Goddess Skill, Shrink. Only a slight flaw, but a flaw nontheless.
Priest (Rest) is a single target debuff, which only weakness is that it can't be used premptively to work. This means that a slow player will rarely get this skill to function.
Seer (Predict) is a single target skill of it's own branch* that's only weakness is the speed of the character being targeted.
Ultimately, they all have strong, and weak points. But some I think (Warrior, and to a lesser extent Wit and knight) have more weak points than others (Priest, Seer) while one at least (Killer) seems to have none at all. Once again though, this all depends on your team, their element and build; so I guess the best thing anyone can do is judge for themselves, now you have the facts.
But above at all its only an opinion, a different combine of 4 ppl in team can make a different result
The rest of all is back to the player to combine it all