Style isn't nearly as important as instructors and your desire to improve.
Even doing kukki-TKD (what you see in the olympics) you'll learn to take hits.
Learning Muay Thai you may not learn takedowns.
Sport BJJ schools may not teach you self defense
If you want self defense, find a good or even decent school that focuses on it regardless of art, and put in some time outside of class.
How an instructional class goes doesn't define how a practitioner trains.
That sad,
In the 4 years I've been training I've used it 6 times. I only kicked twice, for a leg sweep. I could have went for the side kick to the ribs, could have front kicked the chin on one of them. But, that would've created massive liability for me.
The first time I ever used it was against a drunk frat boy, he tried to clinch and I knocked him out with an elbow and fractured his jaw. Found myself in the police station getting a talking to about how with my training I over did it since it was just a drunk idiot, not another real threatening situation.
I never had to go to court, no charges were filed for either side, and I haven't seen the frat guy since. But I did have to spend the night at the station, and they could have charged me with battery.
It sounds bogus, but if you ever have a lawyer of LEO tell you what you are allowed and aren't allowed to do it will blow your mind. (This is in OH, your state may be different)
Liabilities of things like head and body kicks aside,
You aren't going to be told to use them in SD, I've never seen anyone advocate sport style TKD sparring for SD, you'll learn to fight with your hands, to do locks, throws, clinches, etc.
regardless of what you train in or how often, you need to be working with as many styles in as many ways as you can.
A style doesn't defend you, you have to practice, spar, drill, and do it yourself.
It's all in how well your instructor can teach and explain things to you, and how much effort you put in