For biceps growth
For biceps growth, the two are close. Preacher curl rates slightly higher: more stretch.
Dumbbell curl is easier on the joints.
Both are good choices that train the biceps the same way, so they swap freely. Rotating between them every few weeks is an easy way to vary your training.
The research score comes from these, scored by hand from the studies. Lifter scores appear once an exercise has 10 ratings. How scores work
Dumbbell Curl. Simple and joint-friendly, though tension fades at the bottom of each rep.
Preacher Curl. Big stretch, but bouncing out of the bottom is where elbows get tweaked.
For biceps growth, the two are close. Preacher curl rates slightly higher: more stretch. Dumbbell curl is easier on the joints. Both are good choices that train the biceps the same way, so they swap freely. Rotating between them every few weeks is an easy way to vary your training.
About the same: both are easy to learn.
Dumbbell curl needs dumbbells, so a home gym covers it. Preacher curl needs an EZ bar and a bench, so for most people it’s a gym exercise.
Dumbbell curl: it rates Excellent for joint and recovery cost in our research rubric, against Good for preacher curl.