The Writer's Handbook provides the comprehensive listings writers need, including publishers, literary agents, writers' courses and prizes. These are interspersed with useful essays, eg about tax and the writer. Much of this information is invaluable; a couple of hours' research on, for example, literary agents or publishers may save you months of wasted effort submitting work to unsuitable recipients. If you're serious about getting published, you need either this or the "Writers' and Artists' Yearbook".
Which is better? Personally, I prefer the Writer's Handbook . But in terms of content, there's not a great deal between them. If you're unsure, check out both in a bookstore and see which layout and style you prefer.