What kind of protein powder should I purchase if I don't go with the BioTrust brand?

Best guideline for your protein powder (or any supplement) is the quality of the brand. BioTrust is great. So is Bullet Proof or Sunwarrior.

Your protein powder should be mostly protein (aim to get about 20-30g protein). Very low in carbs (less than 5g). Typically they have no fat, however, some (like Bullet Proof) might, and that's ok. Aim for less than 3g of fat.

Bullet Proof and Sunwarrior are my two personal favorites.