i was just watching an episode of a jacques pepin show, i think it was "fast food, my way", and he mentioned the green sprout growing out of garlic. he said that he was always trained to remove the green sprout, and even the core of the garlic clove that it attaches to (because it was bitter), but then he said that he has never experienced any problem with it, and some cultures even prize garlic sprouts as main ingredients.
edited to add: also look for hard neck, or stiff neck garlic. it will have a somewhat purple-ish appearance, and a woody stem in the center, instead of increasingly smaller cloves. i've found it to be much tastier, and less bitter garlic.