You need to consider many different questions when deciding what kind of sailboat is best for you. Start with this article on How to Buy a Sailboat. If you know the general type of boat you want, go here to find available models and learn more.
Depending on the general size range of the sailboats you may be interested in, you may need to choose between fixed-keel boats and centerboard (or swing keel or daggerboard) boats. This article will help you choose which is best for your needs.
As only a very general rule, most sailboats over 20-something feet have fixed keels. Most sailboats under 15 feet or so have centerboards. But there is a wide range of boats from 12 to about 25 feet with either a fixed keel or a centerboard. For example, in this photo the boat on the left has a fixed keel, while the boat on the right, of about the same size, has a centerboard.
If you are shopping for a sailboat in this range, you should understand the differences between these fundamental types of keels.
Continue for the benefits and disadvantages of centerboards and fixed keels.