It is interesting how people have different interpretations of the word 'influential'.
Does most influential mean that the person brought martial arts to the forefront of the public mind through the media?
In this case it would have to be Jakie Chan who is apparently the most famous person world-wide full stop. Bruce Lee is more popular in the West because of the more serious bent to his films and life (JKD itself might not be considered as world-changing as a lot of people believe it died with Bruce Lee's passing)
Or....does most influential mean to have developed martial arts/thinking in a physical way, out of the media spotlight?
Ueshiba and Kano Jigoro have to be the two big hitters with probably even numbers practising their consecutive arts. Karate is also very big but was way ahead during the 70's and not so now? (not sure about this one) . I don't know if one man is responsible for the birth of modern karate?
I also heard TKD is now the biggest martial art, but I don't like it so there!
Ueshiba's deshi have to also be very influential and it seems it depends on location when considering who's style is the biggest. In the UK I think Tomiki is probably the biggest, with a strong following in Japan, especially Universities. In France Aikikai has the largest numbers by a log way. In the US I don't know, but I think the Ki development society has to be up there.
Yoshinkan is widespread, but it seems very big in Japan esp. in terms of armed forces training.
Okay, I just read my post and I've been going on far too long, so I'll shut up now