I am a fan of Muscle Milk. All of their products are good quality, and they taste VERY good, perhaps the best out there; but my favorite is the casien protien. They are one of the few to market a casien specifically. Casien is protien found in milk, and it is a long lasting protien. Meaning that it takes a long time to break down in your system, which is why you take it just before you go to bed so that your body has a nutrient supply while you sleep.
As to their whey protiens, you cannot go wrong with them at all. they taste great, and they can be had for a fair price. I've a cabinet full of their stuff.
I go between Muscle Milk whey and a whey from www.allthewhey.com
There are two kinds of whey, isolate and concentrated. The difference is that isolate is more "pure" in that your body will absorb about 95% of it, and with concentrate, your body will absorb about 75 - 80% of it. IF you're getting enough protien, thats splitting hairs.
Enjoy