Looking through a reference site... Can't see much difference between the straight bar and EZ bar.. But the hammer curls and Dumbell curls are different..

Straight Bar Curls

Muscles Worked:

Barbell curls are a compound movement. The primary muscles involved are the biceps. Secondarily are the forearms, traps and shoulders.

Muscles Worked:

The primary muscles worked are the biceps. Secondarily are the forearms, traps and shoulders

Seated Dumbbell Curls

Muscles Worked:

The primary muscles worked during seated dumbbell curls are the biceps. Secondarily are the forearms, traps and shoulders.

Hammer Curls

Muscles Worked:

The primary muscles worked during hammer curls are the biceps, especially the brachialis, and the forearms. Secondarily are the shoulders and the traps.