According to
http://www.ncbi.nlm.nih.gov/pubmed/20977230:
protein source PDCAAS (%)
casein 100
egg white 100
beef 92
soy protein isolate 92
chickpeas (canned) 71
pea flour 69
kidney beans (canned) 68
dehulled hemp seed 61
pinto beans (canned) 57
rolled oats 57
lentils (canned) 52
hemp seed 51
hemp seed meal 48
whole wheat 40
almond 23
PDCAAS = Protein Digestibility-Corrected Amino Acid Score. One reason hemp scores so low is because lysine, leucine, and tryptophan are all limiting amino acids, meaning hemp is not a complete protein; our bodies utilize protein only to the limit of said limiting amino acid. The effect on you depends on your diet.
At the end of the day whey is cheaper, a complete protein, digests quickly (vs casein), and has a lot of research backing it.