Krav maga is only good if you have decent instructors. A lot seem horrible unfortunately since it is a great defense art. BJJ is horrible for self defense or practical use. You can adapt some things but overall it isn't good for defense training. It's a hell of a workout and a great sport though. Muay thai is only slightly more practical BJJ since you are staying on your feet, but it is also one dimensional. Just like BJJ, hell of a workout and a great sport. An MMA class isn't practical for anything accept a good work out and guys training in BJJ, Muay Thai and that want to practice MMA.