So here's my hypothesis and recommender of each classes.
Swordsman:
Strongest DD in game with lowest DEX/AGI, probably most suited as shura from shura's high attack and endurance/vitality.
Thieft:
Fastest class in game with avg. attack dmg and quick attack, probably have ability to turn invisible. Most suited for human in my opinion, human got decent damage and good AGI/DEX.
Doctor:
Yay, Doctor = heal nonstop, ok, so Doctor is healer, we all know that. Recommend you become doctor as a sylph, sylph got the most INT/WIS(or CHI, I think Chi is what it is in this version) of all 3 races.
Mercenary:
Tank/DD person, able to use all attack weapons like dagger(theif's weapon), swords(swordsman's weapon), axes, spears. Probably an all around class though. Any race should be able to be good as mercenary.
Wizard:
Ok, spam your skills and kill your monsters. Use sylph for it, since you gotta spam skills. Have probably highest attack with super low HP. I recommend shura as well if you wish from its vitality/endurance, but does less damage probably.
Martial Artist:
Tank. High defense and HP. I recommend human as MAs(Want to shorten it
), they have decent endurace/vitality, attack, and good dex/agi for dodging and reduce hit taken and faster attack. But! If you want to just tank and do good damage as well, be a shura MA, have a downside though, no dodging and slower attack.
Shaman:
I think they are pet users, if they are, just use any race to do it, since they'll use pet to attack with the owner's help. If it's a pet user, sylph will probably be able to assist its pet better using pet heals. shura will be able to help for faster kill. Human is just, in between sylph and shura. But pet user is only guess.
If it's not a pet user, it'll be probably like wizard but more physical. If it is more physical, use human for as humans got decent everything.
Hunter:
Puller and long distance attack. Use any race for this. Sylph will probably be using more skills from it's Chi/WIS/INT. Shura can just hit hit hit hit hit!, high attack and take more hits from it's VIT/END. Human can be both hit and skill user as hunter.
Musician:
Ok, the ultimate buffer/debuffer of the game and with a bit of heal, in my opinion. Will probably be affect my Charisma for better buff or something if there's charisma. If there's charisma, use sylph, highest charisma.
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