When you say 'most influential', its hard to know in which way.
I can see why you think Jigaro Kano is, and I would agree in many respects because he formalised a martial arts system which is well known and practiced throughout the world.
However, if you asked most members of the public which martial artists they know, it would probably be Bruce Lee and Jacky Chan. Although they may not have developed widespread styles (I've never seen a Jeet Kune Do class advertised anywhere, though I know there are some), I am sure they have had a large influence on popularising martial arts in general.
Kano possibly had a very original concept in the way he developed Judo, though it is well known that he himself thought highly of Aikido. Although I'm not sure whether Aikido rode on the back of Judo in the UK (it is still quite hard to find Aikido classes in some areas); it seems to be one of those martial arts you only hear of when you practise another martial art such as Judo or Karate.
Possibly we have a bit of a Western Centered view point on this. I'm unsure of the situation in martial arts in the East which triggered off this big spread of martial arts to the rest of the world - no doubt much of it was due to the film industry, and following WWII.
Also, who initiated the spread of Karate in the West? I don't know about the U.S. but in the UK Karate still dominates the martial arts circuit in terms of numbers (or maybe Taekwondo has caught up).
Both Ueshiba and Kano were obviously well respected for the efforts in martial arts in Japan (they both received prestigious awards for services to martial arts). I'm glad for both of there contributions and the world would be very different without either of them (at least for me!)