While there is no "BEST" it all comes down to what you are willing to do to not only survive, but to disable, up to and including K1LL your attacker. Like some have mentioned above, there could be more than one. Just like learning doesn't end in the classroom and the tests you take can never contain the entirety of questions or problems you will face.
The answer is not likely to be "lateral step/outside chest block, reverse punch to ribs step on knee, face punch follow through." It may be "pick up a rock and smash his skull in." It may be "pull out your knife and say 'come on guys, it ain't worth ya'll getting cut up.'"
All the ugliness aside, there are too many martial arts I can name that will not teach you certain things. It's mostly sport related. A lot of the drills can be used practically, but what then? In my honest opinion, combatives are what you want to learn to fight, maim or destroy. A martial arts system is what you would do mostly for fitness, competition and self defense. Let's not start the "whataboutisms" or "my style beats ___ style." Is the Karateka going to be saying that if he gets a power jab from a faux southpaw boxer? Is the boxer going to accuse you of cheating if you grab a beer bottle or stool?
My answer is get with a school or instructor who understands the ugliness and unpredictability (as well as the stupidity in not trying to find another way other than fight) of actually fighting. I've met a boxer, a wrestler and a Karateka who were able to teach to this capacity and made it clear when a person's size can and does matter and what principles or techniques are less effective against whom. Most traditional martial arts however think mechanically or technically and not tactically.
This is where you have methods of training/learning like LINE Combat System, William Ewart Fairbairn, Rex Applegate (who used a few of Jim Bowe's knife fighting principles), S.C.A.R.S (most of it is training the mental response to a threat or to pain/injuries. For instance, if your finger is broken, you keep fighting as if it's your last shot at life and worry about it later. If you break their finger, they may react in an untrained manner and you can keep wailing on them.), SPEAR system is similar in this regard and more modern, in fact, sever Krav Maga instructors have at least heard of SPEAR. Lastly, service related martial arts systems include MCMAP and USACS. They're a bit watered down, but designed to be train the untrained as fast as possible. I've seen a MCMAP black belt get leveled by a tan belt (lowest grade) that was a boxer of 2 years. Go figure.
Going off of statistics, most people NEVER train in any martial art. Including boxing or wrestling. So even if you randomly pick one and learn how the human body moves, how to get someone to react and to control your reactions at the same time, and to deliver damage with the least amount of effort on your part you're ahead of the curve. Your likelihood of running into Don Frye, GSP, Bas Ruten, Mayweather, Tyson or Eddie Hall are pretty slim. And even if you ran into these guys, you're more likely to get an affable back slapping hug or handshake. Look at most police bodycam footage or footage someone captured of a guy getting jumped. You can easily tell if one person is trained or not.
Pick your poison and train! It lasts a lifetime even if you don't stick with it for life.
