I could usually handle myself when I was younger. But when I was in a fight with a big group of people 2 times, and I lost, I decided it was time for some training.
I got my black belt in Hakko Ryu Jujutsu, a stand up traditional Japanese jujutsu. I made them prove they could stop jabs, round leg kicks, and single leg take downs- the 3 things I am most wary of, before I would sign up.
I was in 2 Brazilian jiu jitsu tournements with no real BJJ training and took 2nd both times based off my trad jujutsu. Since then I have had some of BJJ, Judo, boxing, and kickboxing. I have a dojo in my garage and my room mate is as xepereinced as I am, so we don'ty have to waste all day teaching white belts, we can grab 30-40 minutes when we can and train a little.
I started in martial arts for self defense, but I have learned so much more from it. Interestingly, I no longer got in fights after I took martial arts. I have never been a bully, but I must have been putting off something that attracted aggression before, because after learning some skills, no one approached me anymore.

Martial arts taught me so much about how my body works, balance, and respect. I was very rebellious before. When you are sitting 2 feet from someone that without a doubt can mop the floor with you (instructors grand masters), there is no room for rebeliousness. So I learned to treat people with respect, and an inner balance that I try to maintain always.
I love watching UFC. I find most of the top guys are far from meat heads, are usually very respectful, and are usually well educated in something.
For a beginner, I recommend movement based arts like Cali/ Escrima, kickboxing/boxing. It is very difficult to spring into action operfectly at the perfect time like many traditional arts teach. Right now, grappling is king. If you don't know what to do on the ground, you will be toast. Brazilian Jiu Jitsu or Sambo are comprehensive ground arts.