Is it better to focus on reps more than weights for biceps?

I do 40 kgs barbell bicep curls but I can only go 4-5 reps so I drop the weights by 5-10 kgs and do another 3-4 reps.

Is this effective way to train biceps?

Am I better off sticking to slightly lower weights and targeting 8-10 reps without drop sets?