What the difference
Whey protein comes from milk. Soy is from soy beans.
Some feel that the soy protein is not used as well by the body. Whey is very common in protein products. I wasn't able to handle whey. Just the least amount (1/20th of the normal scoop) would make me vomit. I resorted to soy protein & found I could handle it well. You can buy flavored soy milk & also buy tasteless (well almost) powder to up the amount of protein.
My favorite protein drink was something I came up with- 8 oz of soy milk, one scoop of the powder, a touch of Splenda, & either strawberries or a banana all blended up nice & smooth. Really very good & around 25-30 grams of protein, if I remember correctly.
Dixie