Judo comes in three major forms;
Kodokan Judo; The origional format that included Atemi-Waza (striking technques) with throws, takedowns, groundfighting and joint locks.
Sport or Olympic Judo; Which avoids the kata and striking techniques of Kodokan judo based on the rules of competition. Its also based on a less combative form of "school boy judo" taught in public schools like the west has wrestling teams.
Police Judo; is a heavily focused off shoot of Kodokan Judo that focuses more an ground grappling & joint locks that is used by LEOs in Japan.
Just for clarification, there is only one judo, Kodokan judo. There may be different emphasis put on techniques, but it is all Kodokan judo. The IJF may set the rules for Olympic competition, but it is Kodokan judo. The various NGB may empahasis kata or not, but what is taught is Kodokan judo.
Is that true? I'm certainly not an expert on judo, but it seems as though I've read about a distinction between modern/post WWII judo and pre WWII judo. I've also read about Kosen Judo, my impression being that it's intended to be as close to Kano's original art as possible.
As an aside, your post reminded me of this brief conversation I had with a BJJ black belt. We were talking about Josh Barnett and he mentioned that Barnett's jiu-jitsu was pretty good. I said, "Isn't Barnett a catch wrestling guy?" His response, "It's all jiu-jitsu. If it works, it's good jiu jitsu. You can call it whatever you want."
While I think it's interesting, the practical difference between some arts, such as Catch Wrestling, Sambo and BJJ, have less to do with technique than with mentality and philosophy. Sure, there is an emphasis in Sambo on leg locks, and catch wrestling includes many great neck cranks, but the real difference between the three styles is more about intent. A catch wrestler will not willingly cede top position. He will fight for it, while a BJJ guy might actually draw a person into his guard, choosing to fight from bottom.
But all that aside, on a strictly practical level, I think you will find that japanese jujutsu schools as a whole will be more comprehensive in their curriculum, including strikes, kicks, joint locks, throws and perhaps weapons. They will often be formal and sparring may or may not be a part of the curriculum, with very little to no competitive element.
Judo, as typically taught, includes
some formality, teaches very little if any striking and emphasizes at best a balance between standing grappling and groundfighting or newaza. There is an active competitive element to judo if you desire it. Randori/sparring is integral to the training.
BJJ as typically taught tends to be pretty informal. Very little in the way of ritual, and your gear or kit centers on function over style. Where in Judo, you will most often see an unadorned white or blue gis, in BJJ you will seldom see an unadorned gi. While in international competition you will only see white, blue or black gis, outside of that there's no telling. Purple, yellow, even tie-dyed gis... I've seen them all.
So, basically, what are you looking for? What suits your personality? My own opinion is that the best, most effective martial art for you is the one that you will continue to train in over a long period of time, the one you enjoy. Everything else is extra.