Which protein powder should I buy if I'm trying to cut? Optimum Nutrition Platinum Hydro Whey, Cellucor Whey, or Jym protein?

Being in a caloric deficit(eating less calories than your body burns at rest) is more important than what protein powder you're using.

I've found that Optimum Nutrition(both Gold Standard & Hydro Whey) is the best when it comes to taste and mixing. However, don't make the mistake of relying on supplements for your overall results. Building muscle or burning fat comes down to the amount of calories that you're taking in each day.

Phase 8 protein is a mix of whey and casein for the instant and long lasting protein in the body, If i was cutting i would switch to this to continue to produce and repair muscle while cutting body fat. Mainly to cut its just diet changes and more cardio

Protein shakes have little to no influence when it comes to cutting (they do, but they all work pretty much the same)