"kweh" sounds the most natual, so I'll go with that, "Wark" sounds more like what someone doing Chocobo, impersinations would do...
Wark! (FF7)
Kweh! (FF9 and onwards)
Coooc coooc! (FF4)
...eh? There's another noise? (Other)
"kweh" sounds the most natual, so I'll go with that, "Wark" sounds more like what someone doing Chocobo, impersinations would do...