Which exercice do works best your Arms???

well dude do chin up with hands 6 inche apart ,with pamp facing u and also with pamp facing the other way ,its good i tell u

Bench press is more for your chest than your arms. I find that machines aren't the best thing for building muscle. Try using dumb bells, or bar bells as they make you use more uscle. The tricep is actually bigger than the bicep so make sure you work it as well. Try exercises like Bicep Curl, Tricep Extension. Hammer Curl, Skullcrushers. Don't forget your shoulders. Do shoulder press, front raises, and lateral raises.