I think this will probably end up being at least 3 parts for me to cover everything I want to. I 'll start here with my thoughts on self defence training in general and then will get on to whether there is a big difference between "street" and "sport" jiu-jitsu and talk about my own experience of a "real" fight.
Before I go further, I want to say I'm ignoring weapons. To be able to defeat someone who is armed when you are unarmed takes a life-long commitment to training for those situations, nerves of steel and a large amount of luck. Luckily, most fights/confrontations that the average person in the UK will be involved in will be unarmed.
So... personally, I have never been interested in training for self-defence. I think that if anyone is paranoid enough that they feel the need to train specifically for self-defence purposes they would be better off just doing their best to avoid any situations which could be dangerous. However, I don't buy into people selling courses on "awareness"... if you're an adult and you don't realise what sort of situations/people could be dangerous then you have bigger problems. Just be sensible, avoid areas you know are dodgy and people who look suspicious. Then going to the other extreme; if you do listen to the things some people say about awareness you would be constantly on edge no matter what situation you're in... which is ridiculous. You can't live your life thinking everyone is a threat. Just be sensible!
But what can you do if you want to be able to defend yourself? First off, the best and safest way to get out of a dangerous situation is to run away, so get yourself fit... most people can't run at a high pace for very long, so if you can do a decent 400m sprint you'll get away from most people. But what if running isn't an option, or you have someone else you need to be able to protect? If you're worried about that then just train in the martial arts (combat sports) which are tried and tested in MMA. Pick a striking art and a grappling art and train them consistently. You won't need to be as well rounded as an MMA fighter, so just boxing and jiu-jitsu is enough, or Muay Thai and wrestling, or kick-boxing and judo... you should get the point by now. I know quite a few people who have been involved in numerous street fights for various reasons and they've all come out of them safely using what people would class as "sport" training... because they're trained to fight.
What about self-defence training/courses? Well, nearly all those that I have seen are rubbish. For a start most of them are not very physical and don't involve full-contact sparring. If you're not used to getting hit or thrown properly then you're not going to get far in a real fight, and people underestimate how tiring it is to fight someone, especially in a situation where adrenaline is pumping. Any training which is meant to be making you able to defend yourself which doesn't get you physically fit is useless. Worse than useless as it will lead to a false sense of security. Also, who is teaching... have they been involved in many, or any, street fights? If not, what experience are they drawing on to be able to teach? A further problem of these types of training is that many are X week courses... unless you're training regularly for a long time you won't develop good enough skills to beat an aggressive attacker. To look at this from a jiu-jitsu point of view, think about the new blue belt; this is a belt which will generally take someone 18 months+ of training at least 2-3 times a week, and anyone who has achieved that will know that a very big, strong and athletic guy on his first lesson without a gi on can still be hard to deal with... and imagine if they were punching you. The point is; technique beats strength alone, but it takes a long time to be able to develop enough technique to do so. You can't train for 10 weeks and think it will help you much in a fight.
Anyway, is there good self-defence branded stuff out there? Yes, definitely. There are instructors who have knowledge of multiple fighting arts and who will teach people general fighting techniques rather than flashy 'they grab you like this and you do this' stuff which will apparently work 100% of the time. There are also useful things to be able to learn which also have good instructors teaching them; concepts on how to mentally switch yourself into fight mode and how to prepare yourself to pre-emptive strike if you think it might become necessary. Check out Geoff Thompson and his fence idea for a great example. I know plenty of guys who train self-protection systems, but they train all the time and they spar full-contact, they don't just do a short course and teach people specific scenario techniques.
So that basically covers my thoughts on self-defence in general, next up I'll go through the sport vs. street BJJ argument...