I think it's great that you're looking into workout classes as they are a great way to get an effective workout, particularly if you are relatively new to exercise and need to gain experience on how to structure a workout of your own. They are also great for motivation as being in a class with others means you are likely to be more focused and 'present' and get the most out of your time.
If boot camp appeals to you then go for it! The key to stay motivated is finding something that you enjoy. I'm certain you will find that the class is attended by people of all shapes, sizes and ages so you needn't feel intimidated. In fact you are likely to find others will be supportive and encouraging; you're all in the same boat after all. Even if you do feel out of place at first, you will soon settle in and believe me, everyone there is far too focused on what they are doing to be worrying about whether you look a little out of breath. Just go at your own pace and forget what those around you are doing. It's no competition.
Also, got to give a shout out for zumba... I have tried every kind of workout class you can think of (I'm a PT) and zumba will always be my FAVOURITE. The most fun I have ever had working out