I feel that both are very important1 !
Initially when we are a greenhorn we should go with the lighter weights and make more reps.
Once we get accustomed to the weights we could have heavier weights and for small reps.
Lighter weights more reps - gives a perfect shape for your body since you make a to and fro motion for longer time and it is very important to get shapes in earlier stage.
Big weights lesser reps - builds up your muscle and make them bulkier.

Thanks for the question and happy gymming :)