Though I havent taken it personally, boxing is very very useful. it teaches footwork, and what to do with your hands.
Capoeira is very unrealistic. Elements of it are nice, but using it solely is too sporting to get anything done. It's more flashy than anything.
Mixed Martial Arts is the best way to go. Sticking with one style solely serves to make a predictable and rigid fighter while dabbling into multiple grants you more insight into what your foes might use, more techniques to choose from when optimizing what works best for you, and offers means of covering for potential weaknesses. Cross Training with other physical activities also serves to empower your combat ability as well.
My foundation roots from Tae Kwon Do, but if I expected to succeed with solely that I'd be an easy target. I also have elements of Wing Chun, Muai Thai, and Karate alongside years of dance, ballet, theater (body language, falls, feints), gymnastics, parkour, elements of psychology (tells, feints, and a foe's predictability), and a little bit of weapon's training (kali sticks mostly). I've also taken some Krav Maga classes and learned a little Capoeira (as well as some kung fu, but the instructor was a joke who was doing it to impress chicks, so I barely count it), but I've incorporated next to nothing from those two.
I overall am pretty rusty, but each of the times I've bothered retraining I've seen that most of what I've learned has stuck around. Despite this background, word fu's the best fu.
Choy lee fut! It's a kind of kung fu, a shaolin offshoot, and it's fun to do. It's also not that difficult. It places pretty even emphasis on striking and locking, so I guess it's rather well rounded, except its sort of weak against ground & pound/judo/ju jutsu, and other styles that make use of wrestling techniques. It also covers working with/against a few different types of weaponry.
I couldn't find any videos without somewhat silly music, but nevertheless here you go.
I don't practice any asides being a lethal tan belt ninja with razor sharp knife hands.
The one im the most interested in is Wing Chun. The Martial Art that spurred some of the 2 greatest martial artists of all time as well as having one of the most inspirational back stories to its creation.
The kempo master is insanely fast and it's obviously from years of relentless focus. He obviously makes it look good, even though I don't really like the demonstrations tend to be on a target which doesn't actively defend or react. But the blocking and strike technique is interesting with the snap and fast strike-impact-stop, transferring kinetic force so focused and tight. Not a strike through a number of martial arts train.
It also seems to help change motion quick with using the other arm.