Knowing which protein is better is impossible without the nutritional info.

Generally speaking, check the label to see how many grams of carbs and fat there are in each one, compared the grams of protein. Based on the label of PWO (post workout) shakes I trust, you want close to or more than 30 g of protein right after a workout. Whey protein is good then. There are plenty of proteins on the market that have less than 5 g of carb and a couple g of fat. These are the protein shakes you want PWO, if your goal is fat loss. Other protein shakes are better as a meal replacement. These shakes will have higher level of fat and carbs. In a meal replacement protein shake, it also nice if some of the protein is in the form of caseine. This is a slower digested form of protein that will keep supplying protein to your muscles, and keep you from getting hungry as quickly. The biggest concern I think you face, given your goal of fat loss, would be taking a protein shake that’s chock full of calories from sources other than protein.

Preworkout, if you want to have a shake, that’s not a bad idea at all. If you do so, having a few more calories from carbs and/or fat aren’t so bad because they’ll help fuel your workout.

There are many, many threads out there on the interweb just waiting to be googled on this subject.