I think Judo has some applications for self defense but it should be combine with another type of art that incorperates strikes. If you are going one on one in judo match, that is one thing. If you are in a street fight, you can't afford to put a submission hold on a guy unless you want one of his buddies to pound on you.
I did Tae Kwon Do for a few years when I was younger. I feel it is one of the easiest arts to apply even at a low level. Although I like TKD, the proportion of kicks versus punches is too skewed. Some people where I trained only used their arms for blocking. Another thing is that if you end up on the ground and all you know is TKD, you better get up quick or else you're dead meat.
I'd say a combination of these two would be pretty effective in most scenarios. Either that or TKD and Jiu Jitsu.
The ATF should be a convenience store instead of a government agency!