Would Vitamin C cream be better or an ampoule?

I would like to try using a Vitamin C product for whitening.

A really wide variety of products were coming out.

At what stage is it best to use Vitamin C products?

I would like to use the entire line together, but since it might not be a good fit, I would like to try using just one product first.

I am wondering which stage of product is the most effective.