It depends on very situation. If they are both adverbs then they have the same meaning. But if both aren't adverbs then they have different meaning. Here's what I mean. apiece is an adverb, that is represented for each piece, thing, or person; for each one; each: For example: We ate an orange apiece. The cakes cost a dollar apiece. And if "each" is not an adverb. Each as an adjective: Every one of two or more considered individually or one by one. For example: each stone in a building; a hallway with a door at each end. Each as a pronoun: Every one individually; each one For example: Each had a different solution to the problem. Each as an Adverb: To, from, or for each; apiece For example: They cost a dollar each. Here are some synonyms of "Each" that could give you a better idea on it. Each, every are alike in having a distributive meaning. Of two or more members composing an aggregate, each directs attention to the separate members in turn: Each child (of those considered and enumerated) received a large apple. Every emphasizes inclusiveness or universality: Every child (of all in existence) likes to play. Website: http://dictionary.reference.com/browse/each

It simple says that a happening will be much worse than what you have already experienced,

Letter A has more sense on the book's insight. It already gives the readers the idea of what your book is all about. Letter A represents the main idea of the book. So, it will be much better.