Blade & Soul's NA and EU official site has been updated with new class information, including class descriptions, major skills as well as difficulty. Kungfu Master is the hardest class, as the official site marks "expert" for this class.
Kung Fu Masters can control the flow of combat through use of combination attacks, stringing together a long chain of blows one after another. While they are capable of facing multiple enemies at once, leaping and pouncing from one foe to another, they are most effective in one-on-one combat.
The Kung Fu Master’s greatest strength is how well they cooperate with other warriors. By leading the charge, the Kung Fu Master can force an enemy into submission while teammates pour on the damage.
On the other hand, Summoner is the easiest class and recommended to new players. It's also the most lovely class with the ability of controlling a minion who fights alongside him/her.
Blade & Soul is going to start beta test in NA and EU later in the autumn.