Which is stronger Tg Tae Kwon Do or martial arts?

Each person is going to have their own opinion, and one art is not inherently better than another. It depends on the quality of instruction, and the skill of the practitioner as to the effectiveness in real life self defense. You need to decide what you want to do. It is best view a class of each, and make your own decision. Some schools of Taekwondo differ greatly from other schools of Taekwondo. Some are sport oriented, and may appear to be just about competition. Other schools are toned down to be family fun oriented training for the kids, and their moms and dads. Authentic Taekwondo is very deadly, and those that train in a "Reality-based" school will have a much more intense program.

Those that train in Krav Maga will often desire the straight forward approach to fighting with a strong focus on just the techniques needed to win in self defense. A typical Taekwondo program is more rounded out with a balance of material that supplements the whole mind, body and spirit aspects that are not directly related to physical combat, but support the training of the student as a whole. Whether either one is "better" is up to the individual to decide, but a skilled practitioner of either art can be just as deadly and effective in self defense.