Costume with crests are available on the A31 client! What are these crests and what should you go for?
You should generally aim for 2 types of costumes, one to tank with and one to attack with.
A typical Attack costume would look like this: Flat HP/Shield recovery Greens(Or 1x Movement if u need the MS), % PK res Blues, % % DK Attack Purples & % PVP DMG Bonus.
A typical Defense costume would look like this: Flat HP/Shield recovery Greens(Or 1x Movement if u need the MS), % PK res Blues, % DK Attack Purples & % PvP Dmg Res Orange.
(Note: Be sure to check your current DDR & PVP Res, a character cannot have over 75% in either, anything over 75% is useless!)
(Note 2: Any crests that are not in the above lists can be used, but it would not be optimal!)
Some fancy having a leveling costume wich would consist of EXP crests greens and PVE DMG res Orange, especially for endgame such costume would come in handy!