Each class is so different, it is very important to find the class that fits how you want to prepare early so you have time to take it before birth. Just like how they are all different types, each class has a different length, anywhere from a weekend to 12 weeks to all through pregnancy.
The one piece of advice I give though, is know that in labor, please throw out anything that isn't working. You do not have to stick the program you learn. If it isn't working, try something else. Your body knows what to do, and sometimes the program you pick isn't what it wants. It's wonderful to have a plan and work with it, but some of the methods just don't work for everyone.
1. Hospital Birthing Class
This one most know about, especially if you are birthing in the hospital. It is taught by either a childbirth educator that works with the hospital or a nurse at the hospital. Most are 6 weeks long, for about 1-2 hours a week. They aren't very information intensive, but you will learn the basics about birth. Most of the class is about hospital procedure and protocol and all the pain relief options available. They do not spend much time on breastfeeding, and most will not give specifics about the rates of interventions at the hospital. They will do a tour in one of the classes, which is nice to see before you go into labor, but you can do that on your own without going to this class. The majority do not teach ways to cope with labor, which is essential when planning a natural birth. Learning that it is possible and ways to help it along will boost your confidence in yourself, even if you end up in the heat of labor throwing it all out the window.
2. Birthing From Within
This class, and the book, are excellent if you have any hangups from previous births or information you have received. The class is mostly about learning to control your fears, figure them out, and move forward with your plan. With the book, it does talk a lot about how the pain in labor is a fine line that only some women can endure, which isn't helpful at all when planning a drug free delivery. The class is a little bit different and varies with instructors, but a lot of it is about working with the fears you have. Fear can inhibit labor, and learning to address your fears and work with them can make your labor and birth a better experience. The class is normally 6 weeks long, but again, varies between instructors. If you want a class that can help you overcome past issues surrounding birth and help prepare to make your next birth better, this class is excellent. Even if you don't want to take this class, just getting the book if you have fears to overcome can help immensely.
If you want to go the way of hypnosis in labor, this or Hypnobabies below is for you. Hypnobirthing prepares you for a gentle birth, with minimal pushing and lots of self-hypnosis and deep relaxation exercises. This program is based on the belief that childbirth does not have to be painful if the mother is completely prepared and completely relaxed. I've seen this program work, but for a lot of women, labor will not be completely painless, even with total preparation. This class is five weeks long, with classes that are 2 1/2 hours long. You are supposed to keep practicing the hypnosis and relaxation exercises inbetween and after the classes so that you can be fully prepared. This is a constant technique, and it does take practice to learn. Practicing by yourself without instruction can be difficult, but if you are able to achieve this, it is worth it.
This is similar to Hypnobirthing, with six week classes, but they have CDs you can listen to at home to help you completely prepare. They also have a self-study program where you just buy the book and CDs and do this on your own time. The best part about Hypnobabies is that you can start this early in pregnancy and completely prepare yourself all the way through. It isn't just a class, and they have tracks specifically for a lot of situations, like cesarean preparation, turning breech babies, mothers with previous loss, and much more. I highly recommend this program is you are going the hypnosis route.
5. Bradley Method
This class is made to help partners become more involved in the birth of their children. It is a 12 week course, the longest there is, and it focuses a lot on nutrition and kegels. The best part about this class is how in depth it gets because of the amount of time you have with your instructor, and if your partner (or yourself) needs to know more about birth, this class is excellent. Nutrition is key to a healthy pregnancy, and this class really stresses that point. If mother is healthy, then baby is healthy, and that is key to a healthy pregnancy and delivery.
This class isn't what is depicted on TV or the way your parents and/or grandparents say. It isn't about breathing exercises anymore and focuses more on education. It is a more basic class than some, but you will have 12 hours of education. It is an evidence based course so you will learn research and evidence about each practice used, but it doesn't teach ways to truly cope with labor like other classes based on these methods. You will learn about practices used in birth, which can be really helpful if birthing in the hospital.
This is also a more basic class, but you will learn evidence based research on everything. You will learn how to make decisions for yourself, which is a skill necessary for birth. Each teacher does teach a little differently, but the content is the same. You will learn all about pregnancy and childbirth, which is great if you aren't as knowledgeable as you would want to be.
This class is run differently depending on the teacher, but the basis is complete preparation for birth starting with a healthy pregnancy. The instructors are trained to know a lot about birth, so even a knowledgeable person can learn things from this class. You will learn ways to work with (and cope) with labor, the different aspects of birth, and all of it is evidence based. The classes vary in length, but most are six weeks long.
9. Independent Classes
There are other organizations to certify or work through, or sometimes you can find someone that teaches their own childbirth class. Find out all you can, but they don't have a set structure for each class so no real comparison even if two teachers have the same training. Find people that have taken these classes, and talk to the instructor about what is discussed and learned. These classes can be better than any other depending on what you are looking for. Sometimes these classes are offered from your doula in a weekend crash course, so you don't have to make weeks of commitments but learn with the person you are having support you in your birth.
And please remember, no matter what class you take or what method you learn, you can throw it out if it isn't working. Do what feels comfortable to you.