What should I take ? No Gi Brazilian Jiu-Jitsu vs Muay Thai Kickboxing?

They each have pros and cons; neither is better or worse than the other. The major difference would be that in jiu-jitsu, much of the emphasis is on flexibility and agility; Muay Thai is a about pure brute force, getting as much strength behind a fist, knee, or elbow as possible. Both are great for getting fit and losing weight and would help you to hold your own in a fight. However, if you feel like you want to focus more on increasing agility and whatnot, jiu-jitsu would trump it; if you want to build muscles faster, Muay Thai would be better. Have fun!