Somebody asked this question on Quora, and I answered it like this:
The most relevant comparison of these great martial arts is to relate them to your own specific goals. Are you trying to select one style in order to devote yourself to training? If so, are you training to win competitions, or defend yourself in an unanticipated street altercation? Or is it a conceptual, intellectual analysis of these arts?
Each of these systems have extensive sportive applications for all sizes, ages, and levels of experience. You can train to compete and win all kinds of medals, trophies, and belts. With a competition mindset, you can experience gains in strength, endurance, and positive changes to your body composition.
Each of these arts also have combative applications, and depending on the particular local school you choose, you can learn to effectively survive a street fight against a single opponent. Even though, strictly speaking, Judo and Sambo are sports, there exists many Combat Judo, or Combat Sambo, etc., which will prepare you to defend yourself. As for BJJ, Helio Gracie, a co-founder of Gracie Jiu Jitsu, designed his style of Jiu Jitsu for the purpose of self-defense.
No matter what conclusion you make about these styles in general, it is the specific school you train in, and the quality of the instruction, and your peers in that school which will determine your actual effectiveness. Bad versions of any those aspects, no matter what the style is, will limit your effectiveness. And of course, the level of dedication you want to apply to your own development is the remaining factor.
If you’re just trying to make an objective, qualitative analysis, it’s hardly useful to compare. There are super effective practitioners in each art that show this. Bruce Lee said, “Man, the living creature, the creating individual, is always more important than any established style or system.”
A good line of inquiry might be, “Which of these arts would best enable me to fulfill my personal goals and is there a good school nearby where I can train consistently in?”