Which protein powder to buy?

You can get into a lot of detail in picking a protein, but to make it simple, following these few guidelines.
1. Whey protein is whey protein. Yes some brands are a bit higher quality, some mix better, some taste better, etc. But for the most part, in a similar cost range, it's all pretty much the same in terms of how the protein is going to function. The rest is mostly personal preference.
2. Whey isolate and whey hydrolysate will help if you have lactose intolerance or issues with whey concentrate. Otherwise, it can be just fine to get the whey concentrate. Again, it's all whey protein.
3. For a pick at Walmart, do not buy any protein because of what the label or someone claims. There is no magic fat burner protein. Protein can be used as part of your plan, but once again, protein is protein. Look at the grams of protein per serving, and figure the grams of protein per dollar. That really should be your primary factor until you try one and decide you don't like it due to whatever personal preference.

If you're into extreme health science or serious bodybuilding where the details matter, it's worth researching into it further. In those cases, the absorption speed, anabolic response, and other such factors can make a difference. Otherwise just pick one with the few simple guidelines above and stick with it if you like it. Of course you can try others too for preference reasons, but it's not going to make the difference in the weight loss so long as you simply have a decent protein, one brand or the other.

If you have any further specifics in mind on how you want to use the protein, there might be some further helpful suggestion. For example, if you know you want a certain amount of protein per server, look closely at the service size and total servings per container.