The first ingredient must be protein, and it will say exactly that. It might say protein derived from whey, soy or egg whites. Make sure it doesn't say fructose, glucose or sugar. Soy protein has been shown to prevent the risk of developing breast cancer in women, prostate cancer in men, and has been shown to lower blood pressure and cholesterol levels naturally. Many body builders prefer whey protein for their meal replacements.
Some people prefer protein from soy or whey to egg whites.
It depends on what you are trying to do. I personally consume soy protein everyday as a prevention to cancers. Two scoops will give you 26 grams of soy protein that has been through a fermentation process. This assures that you are getting the best quality soy. That is because we are not all made the same.