Pull up and Chins. I always felt my grip/arms giving up on them well before my lats so I dropped them.
Mentzer thought curl grip pullups or pulldowns were the greatest bicep exercise. Arthur Jones might have said it before him.
Edit. Just a set of dips and a set of curl grip pulldowns would maximize your arm size potential in 2 years. Ad only 400 hours of total training for realizing full muscular potential. He might not have been far off.
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/http://arthurjonesexercise.com/MuscleTraining/FourHundredHours.pdf