I would say both are awesome.
Duke personally is better for me.On PvE its do better since its the most defensive character on game,faster combos,well bossing and annoying on pvp.
Gambler is awesome to,better on grinding,more offensive,boss well.. but on high places like 60+ Floors on CT it have a hard time killing.
PvP Gambler is a little better since do more damage usually if go HP.And since HP is the best choice for PvP a HV Duke keep a little down comparing it to gambler...But its just a style of play I like I mentioned before prefer Duke but its up to you.
Volley Kick,Siren Song and Sumo Suit are away to cool xD.
People will eventually love me :3