Does anybody actually train mma/bjj/no gi/etc for self defence?
I kind of think that most people train because they enjoy the relevant activity, and there is an additional bonus of being a bit better equipped to cope with a self defence scenario (although I think these scenarios are extremely rare unless you deliberately put yourself into confrontational situations)
The first line of self defence is to walk round looking confident (and maybe a bit muscular). Judo certainly helps with that, as do most grappling styles. I think Judo has a special advantage for self defense though, and that is that a good Judoka has a really good base while in a natural standing stance. Many incidents start with a shove or a grab. In my experience grabbing a Judoka (of higher level than me) is a bit like trying to unbalance an oak tree, you can tell you are in trouble the moment you touch them, and sometimes before you touch them. Judo can potentially save your life before you even realise that it was in danger.
Judo is fantastic for self defence. A close second to BJJ
The best form of self defence is to attack first ; )
To be honest I think training any martial art with the belief that it will teach you moves to fend off multiple attackers is just stupid. If enough people come at you at once you are fucked no matter what. I do however believe that training in any full contact martial art as well as competing give you the best possible advantage in such a situation as you learn to handle fight or flight reflex, adrenaline dumps etc. It just helps you read situations better and think clearer in such a situation.