It is called BV - Biological Value. This is a figure representing how 'bioavailable' a protein is to your body. Egg Yolks and Whey Protein are very, very high. Peanuts are on the low side, along with bread (both around 55-60) whereas Egg Yolks average 105 and Whey even higher. Don't be fooled by ridiculously high BVs -- tests on many of these supplements have shown their true BV to be
far lower than represented. Also keep in mind that all Protein is "good" for the body. Some proteins are just "better" in terms of the body's ability to utilize them quickly (remember that there is no lasting protein pool in the body -- it depletes every 2-3 hours, which is the reasoning behind 5-6 small meals daily with protein at each.) Obviously Whey is a better choice than, say, Gelatin, but don't be too overly concerned with the biological value.
As for the "best", that is a matter of opinon (like most anything else

) ... I personally use and recommend Optimum Nutrition 100% Whey. I use the strawberry flavor (sweetened with acesulfame potassium) and it tastes great, even mixed with tap water. I usually mix it with sugar-free kool-aid or a glass of ice cold skim milk for a morning shake (but no milk for now, as I'm on a keto diet

)
And please, don't waste your hard-earned money at GNC. There are several reputable online retailers which sell the same products -- often in larger bulk sizes -- for what you'd pay for a small 2lb. container at GNC. My favorite is Netrition.com, YMMV
