You can't really go wrong with either one, pick the one whose class fantasy you enjoy more, or play both ^^ Both are very capable damage dealers, fun to play and both are good pvp classes. Shadowhunter has two builds by endgame. One is all about demon form, the other outright doesn't use it.

Is Deathblade a good class Lost Ark?

More of a Rogue than an assassin, Deathblade is a highly mobile, melee, damage dealing class that can do both consistent and burst damage. They are unique as they are one the few classes that utilize many charge-based skills.

Is shadowhunter class good?

Shadowhunter in endgame performance is incredible good, including that she is one of the most easiest class to main and cheapest to build.