I was asked to post this for the benefit of others. I will explain what I think the differences are between Jujutsu, Aikijujutsu, and Aikido, based upon my own personal experience and opinions. Please take what is written with a grain of salt. I am not trying to create controversy or insult anyone. Please excuse my opinions, and let me state that I am by no means an expert on these subjects, even after almost 18 years of study. For historical facts, I would encourage that people find online resources and books by more qualified people, as I am no historian.
As I undestand things, Japanese Jujutsu was born on the battlefield (like most combative arts). Virtually all of the techniques, hand motions, and footwork are directly from sword and spear. As some of you may be aware, there are many styles of Jujutsu, ranging from hard to soft styles. IMHO, a lot of styles (especially modern ones) are offshoots of others, reflecting the new headmaster's attitude, beliefs, and level of knowledge.
In comparing Jujutsu, Aikijujutsu, and Aikido, many classify Jujutsu as hard and brutal, which it can be. It was meant for the battlefield and to disarm and dispatch an enemy, and a lot of the techniques break the opponent. I have been told that there are no safe falls out of true Jujutsu techniques. The old Jujutsu techniques I have seen are beautiful and yet scary. What we see now are safe alternatives for practice. In my view Aikijujutsu is a much more efficient execution of Jujutsu — in other words, a higher level of skill. Techniques utilize much smaller motions and have a more devastating effect if executed correctly and with a relaxed body and mind (sound familiar?). Aikido, in truth, is a modern offshoot of Daitoryu Aikijujutsu. The techniques (numbering about 20 standard formal techniques by my count, not including variations) are taken from I believe the first scroll of Daitoryu techniques. I have heard that there are as many as 2,000 documented techniques in Daitoryu, though there are much better historical sources than me.
It is my belief that Jujutsu is not practiced the way it used to be, and the general level of practitioners is not what it once was. Jujutsu literally means 'soft art' or 'pliant art,' which you wouldn't know by how people practice it. A lot of local muscular power is used, which I personally believe probably was not as prevalent in the olden days. As others have stated before, systems can get "frozen in time" and people focus on preserving the rote techniques (i.e., kata) rather than learning how to make the art their own based on their body type, strengths, and personality. I believe that a really good Jujutsu practitioner's execution of techniques would be soft (i.e., without overt muscular power). Even modern Judo looks nothing like the way Jigoro Kano did it.
Aikijujutsu came from the Aizu clan. These samurai developed techniques that were more efficient than low-grade samurai Jujutsu. True Aikijujutsu is hard to find, IMHO. There are a lot of people claiming to teach Aikijujutsu or 'Aiki Jitsu,' but it is usually a mish mosh of joint locks, Judo throws, chokes, and strikes. As I understand it, traditional Aikijujutsu (i.e., Daitoryu) has three levels:
Jujutsu (the basic locks, strikes, throws,etc.)
Aikijujutsu (much smaller techniques where uke adds to his own demise)
Aiki No Jutsu (the 'invisible' or 'magical' techniques)
Aikijujutsu is incredibly subtle and almost impossible to counter because there is no indication of what is coming. And if someone snaps a technique on you really well, you are too disoriented to fall properly. The practitioner is incredibly relaxed mentally and physically, has a very high level of anatomical understanding, psychology, and perfect body usage and breathing. At higher levels, the intent is to use only as much muscular power as it takes to move your own body. In execution, every technique attacks the opponent. There is no retreating.
Some high-level practitioners can literally off-balance and throw someone by the tip of their finger with no joint lock, pain, or injury (except for maybe the landing). Their sense of where you are and where your center of gravity is can be spooky. Because of this level of sensitivity, an opponent can find themselves stuck to their 'victim' entirely by proper angling and body mechanics. Another unnerving skill is when someone is so good they can actually move slower than their attackers, yet evade or intercept all incoming attacks. I believe there is a huge psychological component here, where one is off-balanced by their own perceptions. Some techniques make people choke themselves out or lock their anatomy by creating balls of tension in their body. From my observations, a lot of techniques appear to be designed to create tension in the attacker's body that can be taken advantage of. If someone attacks hard, they get it back ten fold. Now, if someone knowingly relaxes, the aiki might be hard to pull off, but that ability rests on the individual. The subtle stuff is meant for full blown attacks where there is intent, IMHO. If someone doesn't attack full on, the practitioner can always fall back on harder techniques and strikes. It is my belief that almost no one ever truly reaches a mastery level. I feel that is because people by their very nature get caught up in technique. And there is a severe lack of discipline (myself included) culturally and because of the times we live in. People want to be the teacher or master way too early.
There is a lot of criticism about TMA that practice pre-determined techniques (like the Jujutsu arts), which is not entirely out of line. The criticism certainly is not unfounded as most people really cannot perform the techniques as prescribed. So the instantaneous assumption is, "This stuff doesn't work." A true master, in my view (in any discipline), does not rely on rote technique and could care less what you attack them with. The motions and principles are such a part of their body that they can handle simultaneous attacks from multiple directions. It is a quality of movement developed through technique practice, but it is free flowing and very adaptable. But one does not learn subtle skills such as these by "banging" and competing with their training partners. There has to be some sort of cooperative practice to even get on first base.
When it comes to Aikido, my personal theory is that modern Aikido is not practiced as it was developed. O Sensei was a bad Muh-Fuh in his youth. He could kick ass and he was frighteningly strong in his youth. Practitioners nowadays focus on the 'love your opponent' concept and self-development while sacrificing viable technique. My opinion is that it's popularity worldwide and standardized testing requirements has caused the effectiveness of the student's techniques to suffer. There is a lot of focus on blending with an attacker that usually is accomplished by evading an attack or stepping offline and then trying to re-engage. The motions are also, well, huge compared to Aikijujutsu. And there seems to be a lot of redundant motions in some practice methods (though different federations and schools have their own preferences). Aikido is often referred to as a soft art, but I have yet to meet a practitioner who didn't like to put some mustard on their throws. IMHO, modern Aikido is practiced (by many, but NOT all) more like basic Jujutsu (no offense to anyone who practices it — I did for 3+ years and loved it). I just think a lot has been lost in translation and the art has watered down with its rapid spread. And because there doesn't seem to be a huge amount of real study of the technique mechanics and WHY they work, people have to quit practice as they get older because their bodies break down. At 50, they still try to execute the techniques the same way as when they were 20. Don't misunderstand me, there are some REALLY AWESOME Aikido people out there. I just think they are lost in the huge ocean of practitioners worldwide.
The main difference between these expressions of techniques, in my view, is simply the execution or how it is powered. Any technique can be performed hard or soft, but that is up to the individual practitioner's beliefs about what is real, possible, and/or worthwhile training.
I hope that this was beneficial and not insulting to anyone reading it. I am still learning and have a LONG way to go in my own training before I would consider myself 'good.' My hope is that I will get decent at some of this stuff in the next 20 years.