I have read an earlier edition of Campbell and a copy of Raven's Biology of Plants. Both were outstanding textbooks. If Raven's general biology book is as good as his botany book, it will be very good indeed.
I don't think you are likely to go wrong with either one.
I don't have experience with Raven's book, but I know Campbell's Biology very well. Many people seem to like Campbell's books, but to be honest Campbell Biology wasn't my favorite, in terms of how the chapters were organized, the general writing style, and the usefulness of the figures. I'm tutoring a high-school student in AP Bio, and they're using Campbell Biology also, but many of the students find it difficult to use. For a more general biology book, my favorite book of all time was Helena Curtis's "Biology", although it's out of print now.
I recently found this list of biology books on a web site called Mastering Biology (http://www.masteringbio.com/site/books/index.html). I'd assume that most or all of those books are available on Amazon. Please note that the web site is a for-a-fee online learning site, with content targeted towards teachers and students in formal courses. I'm just recommending this as a good list of textbooks that are commonly used in biology courses these days. Of course, just because they're commonly used doesn't mean they're the best, but it's at least a starting point.
As others have noted, keep in mind that the newest edition will definitely be more expensive. But earlier editions generally aren't that different, at least not with one or two editions prior to the current one. If you're not using the book to go along with a particular class, there's no real advantage to buying the newest edition, unless you're really set on having the most up-to-date book cover. :)