Which of the martial arts should I cross-train in?

I've been doing a fair bit of research, and in that research, I came across many unique arts with their own advantage/disadvantages.
Criteria: Self-defense, technique and practicality. Maybe a bit of aesthetic pleasure also. I'm not concerned as to how much training/how hard it'll be, just a short description of them will do.

Choose a fundamental martial art and add to that.
Eg. If ya do Muay Thai or a striking art add grappling like Judo, BJJ or Wrestling.
I train in Judo which is grappling and I cross train in Boxing for my strikes.

I know people who do striking like Kung Fu and do some grappling so they can escape from chokes etc

Taekwondo Self Defense Techniques

Taekwondo Self Defense Techniques

In a street fight, where should you strike with a round kick?

I'm 16, and have done Taekwondo for 5 years, along with kickboxing, MMA, and a few styles of internal Kung fu. I do anything to avoid a fight, but am wondering where the best place to strike with round kick would be? It's the first kick I throw in sparring, no doubt. I sometimes just use punches (jab, straight, hook, uppercut) and that one kick. In taekwondo we were trained to strike at the ribs, but we all know that tkd is purely for competition. In kickboxing, my instructor taught me to direct the kick behind the leg, as he said it was a knock out spot. I think I would prefer this for a self defense strike, due to the fact it would land faster, and have much more power although I doubt it would be a knockout technique. But, I also like torso directed sidekicks, and train with them the most. So, what do you think would be most effective?

The Thai roundhouse behind the leg, right above the knee. It is debilitating. He won't be able to use his leg and it inflicts a great amount of pain and striking force.

I took Teakwondo growing up. Then I discovered Muay Thai when I was 18 through a MMA instructor. Teakwondo made me a strong kicker, but nothing is more practical in a street fight than well executed Muay Thai.

Taekwondo Self Defense Techniques
Self-defense: Defense Against a Grab from Behind

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