It's been said that building big arms, especially the biceps peak, starts with choosing the right parents. While it's way too late to address that problem now, it doesn't mean you can't learn to work with what you've got by picking the right exercises.
When it comes to the biceps peak, that means identifying moves that more specifically focus on the biceps' long head. Of the pair of exercises below, one does that better than the other, but both play important roles.
1. To Build The Peak: Incline Dumbbell Curl
When you set the incline bench to 60 degrees, you're in a position in which your arms are behind the plane of your body. Focusing on the biceps peak, aka the long head, has everything to do with the stretch placed on a particular head. From this position, the long head is prestretched in the start position, meaning it's capable of a stronger contraction than a muscle that's not fully stretched.
The key when executing this movement is to keep your upper arms back behind the plane of your body; pulling them forward in an effort to raise the dumbbells higher recruits the front delts, a common mistake.
2. To Build The Mountain Under The Peak: EZ-Bar Preacher Curl
Ask 100 gym goers why they do preacher curls, and probably close to half will say, "To build up my peak, man!" So are they right? Well, it's complicated.
The preacher bench places your upper arms in front of the plane of your body, making it the epitome of an isolation move. Here, the long head is not fully stretched, making it somewhat relaxed in comparison to its role during the incline curl. Instead, the short head gets more of the stimulation.
But here's the thing: Since the short head lies underneath the long head, building it can effectively push your peak up from the bottom. It's an indirect peak-builder, but one that you shouldn't neglect in your quest.
Recommendation: Do both, but if a peak is your goal, do the incline dumbbell first so you can handle slightly more weight. For both movements, stay in the classic muscle-building range of 8-12 reps before hitting failure, giving your arms the crown jewel to top off your development of bigger arms.