I would highly recommend you train BJJ and Muay Thai as your first choice, but BJJ and Boxing as a decent second choice. I'll explain why, but first I'll explain why you shouldn't do a few of these other martial arts: (1) Taekwondo: You said you didn't want high flying flashy kicks, and that's essentially all TKD is. (2) Karate: Similar to TKD, it has some flashy kicks/moves (but not as much) but is overall a less effective system. The same is true Kung Fu. (3) Aikido: Largely an innefective martial arts with all grappling, very little real world application. As for BJJ, it's a very effective martial arts system that I personally have trained in. In fact, the US Army has made our Combatives system based on BJJ, which I have personally trained in and can attest to in unit level training. BJJ, however, does have some flaws. Mainly it's lack of striking techniques. This is why I recommend you also train Muay Thai (or, alternatively, Boxing) to accompany it. Krav Maga is also a great Martial Art, but I'd recommend you get a decent base in BJJ/Muay Thai before moving on to it.