Excuse me with my wall of text.
Now, before answering which best suits you, I'd just like to know if you're deciding the character you will main or else wise. I saw class and thought you were stuck on advancement choice, but okay.
Now then, the actual textwall.
Nen Masters are a very interesting Fighter class. While all Fighters, save Brawler, perhaps, are rather blands and "realistic" attacks, Nen Masters are really the only ones with all the flashy moves and such. Nen Masters can buff them or their party members, which is REALLY useful, because the Khai buff adds +100% Light damage. That's +100%, 2x your attack. At level 1. Useless against Light monsters, but it's amazing, nonetheless. Stimulating Breath increases your attack speed, and their late-level Tiger Flash gives them a nice electric tiger to go along with punches. In PvE, they are probably a nice substitute for a Crusader, handing out buffs and still dishing out high amounts of damage. In PvP, what Nen Masters lack in attack skill amounts, they put back in with high damage on current skills. Their Suplex Thunder deals HUGE amounts of damage on their level. At late levels, Energy Shield is a very nice looking attack, Doppelganger Blast is sure to annoy the hell out of your enemies, and Raging Light Dragon is an AWESOME skill.
The only down to Nen Masters is, like all Fighters, they blossom and bloom only at level 30 and later. They may hold out, but they don't reach full potential until then.
Battlemages are an interesting class. Of all Mage classes, this is the route to go for PvP. Contrary to what Verde says, I've partied with a few Battlemages, many have yet to annoy me, nor simply knock monsters down. Their Chaser skills are awesome at juggling, and many of their skills are decent enough to help out at any time. It may just be a mentality thing, but many of them seem to try harder than most teammates would. I do not play Battlemage, nor do I do in-depth amounts of research on them, but I've seen my share of PvP videos, and they're a very interesting class. Many players CONSTANTLY HAVE THEM ON THE MOVE. Many of their skills allow you to move diagonally, since they lack major Y-axis range. Their Chaser skills allow you to buff yourself while dealing extra damage after each attack. I'll tell you now, the golden spear-thing is probably the most epic, non-Awakening skill in the game.
Crusaders, I honestly don't have much to say. They're a support class, but with the lightning-thing, they hold off against magic class rather well. I do suggest trying out with Crusaders though, it will be interesting to see a battleSader in PvP.
Honestly, these class choices are interesting ones. Nen Masters are probably at the bottom of the popularity list for Fighter class, while Battlemage is maybe around the middle, but hardly any Mages in DFO either way.
I'm unsure what you mean by Korean style.
You may change the rules to deathmatch, or maybe do a free for all, or all-out team battle, or do individual 1v1 team fights.