What is the most practical martial art to learn?

Krav-Maga, Judo, or Jiu-Jitsu; all will teach you discipline and self-control. But, the ability to get a fight to the ground, over with quickly, or disable/disarm someone could definitely save your life.

I have done Tae Kwon Do, Karate, Hap Ki Do and Krav Maga. They all have some cross over but for me Krav Maga is the way to go. Effective and simple to learn.

The one you will enjoy enough to spend time in regular training. Why are you going to train? Exercise? Self Defense? The Traditions of Budo/Traditional Martial Arts? Pick the Art that teaches what you want and dive in. I recommend not signing any contracts that guarantees a "Black Belt in One year" or some such. Pick a school you can pay month to month and leave when you desire/have to.

BJJ.

Krav Maga or Take a Class / Seminar from Kelly McCann. He is very up front: gross motor skills, simple hand strikes and kicks with basic boxing. Very painful if you do the 3 Day Sudden Violence workshop.

It really depens what you mean by practical? Useful all depends on the person and thier ability. If you mean value it is so different from school to school, instructor to instructor. Each martial art has strengths and weaknesses, and our taste may be complete opposite of yours? Try to do online searches on what it is you are looking for in technique and discipline, make a short list of schools and try each one out for at least a week, a month if possible. Some martial arts are repetitive and boring, some are complex and exhausting, some are prone to injuries, some require lots of memorizing, but you will find one that just feels right. Hard to know what that is unless you try, it is much better to be exposed and develop your own judgement.

Clink Chank Pow

Jiu Jitsu and Muay Thai.

The one you will train in an use. Same as my advice on "what gun", you are just going to have to try a bunch. Everything below is just rambling on that main point.

I've done many different styles over the years, from GoJuRyu, Kempo (both Ed Parker and the Chinese one), Hung Gar (just a bit), TKD, Judo, BJJ, "American Freestyle", MMA, Krav Maga, a few others, and now do Kickboxing. Interestingly enough, I have never had a combatives course. :-) I say this just to point out that I have tried several.

I have liked different parts of all of them, at different times in my life. What I have discovered is that different styles appeal to different personalities, and different body types have different affinities for different styles. The instructor also makes a huge difference, but that is a topic for another day... If you find a style that aligns to both your personality and your body, you will be happier, especially if you click with the instructor. If you are happier, you will train. If you train regularly, you will get good. Within limits. I've never had the hip flexibility to do head kicks of any style. (Through diligent work, I have gotten my kicks up to about chest hight - when completely warmed up...sometimes)

Next, you are going to have to acknowledge your purpose. You said "practical". Practical for what? Conditioning and flexibility? Competition? Your future career as a Bouncer/Bad Ass? (Roadhouse!!) Self Defense? Not being sarcastic, these are all real motivations. If fitness, almost any art, to include Tai Chi, will get the job done. For the record, Tai Chi can ALSO be pretty bad ass, but not as commonly taught & trained. If competition is your goal, Krav Maga will be a poor fit. If your goal is self defense, I think highly of Krav Maga, especially as they tend to do more training in typical street clothes - it makes a great difference in how well you can execute techniques. That kick in the photo just doesn't happen in off the rack Levi's.

Next, you have to assess your attitude. Different arts, and different instructors, have different attitudes to actual combat. Some preach avoid, deescalate, defend, disable, and leave. Some preach "the best defense is a good offense, so hit first. And break him." And all steps along that continuum. NOTE: All will say something along the lines of the first version to someone off the street as that is the "responsible" version, but you will quickly be able to discern actual attitudes.

Finally, you have to assess the amount of effort you are willing to put into it. I think it is fair to say that arts can be placed into “Content then details” and “Details then content” camps. The first will teach you a lot of stuff quickly, and then spend the next several years getting you from “kinda” to “right”. The second will make sure that you are “right” all along, but you will learn less at a time. I mentioned that I did Hung Gar a little up above, it was definitely of the second camp. Hung Gar stylists are freaking phenomenal, but it is a long time until you advance to “now throw a punch”. On the other extreme Krav Maga has you doing disabling moves within a few classes, normally. I would not recommend someone learn Hung Gar for self defense.
Right now, if I had the extra time in the day, I would want to learn Escrima.

I'm partial to Japanese styles. Goju-Ryu was the style i took. I've been looking at a few places here in the DFW area and found several Jiu Jitsu schools (mostly MMA fusion) close by and a Krav Maga school. Although not Japanese, I would still like to learn Krav Maga.