You’d have a lot of criteria to look over for such an open ended question. However, overall I’d say the bicep ladder excercise would be at the top of the list, followed by wide and close grip barbell curls.
Id stress focusing less of the kind of exercise and more into how you are lifting- rep/set/intensity wise.
there are really only so many ways in which an elbow flexes ……
What I like to do is vary the loading itself. Dumbbells, cables, machines with specific cams and tubing, to name a few, all load in different ways in addition to focus on concentric versus eccentric loading.
I have to say the best biceps exercise is that one that is perfect for the activity one is engaging in.
How does a boxer train?
How does baseball player train?
How does a basketball player train?
How does a swimmer train?
It’s important to take into consideration specificity and train the muscle group so that it’s adaptation is perfect for the activity.