Wow I'm so glad this thread got started. Martial Arts and Penis Enlargement are two huge parts of my everyday life and it seems the two are overlapping. Anyway, I have been in the Martial Arts for a long time even though i'm only 18. I have been a long time kickboxer, I've boxed, and continue to wrestle and train Gracie Jiu-Jitsu. I personally believe that if you are looking solely at defending yourself in a night club or bar or on the street a solid striking art is probably the best choice. It will make you the toughest in the shortest amount of time.
When I say solid striking art I'm talking about something where you are constantly giving or taking shots regularly in training. Boxing is good but in my experience you will get hit alot more if you get into a scuffle because lets face it, everyone who tries to start shit at least thinks they know how to throw punches. BJJ is extremely excellent, but i think you will be alot less effective if you are not dedicated to your training. True, someone training BJJ for a month or two can suBathmateit just about any untrained thug, but as far as taking them down or controlling them enough to not get your faced turned into hamburger in the mean time (especially if you pull guard) that takes alot more experience. I would personally choose a solid Muay Thai school, or hard-nosed competitive kickboxing gym, even somewhat over boxing and BJJ for a beginner. There are certain moves like the plum clinch that will give you an extreme striking advantage over just about anyone you can get it on, whether they have previous training or not.
I know my age might seem kinda young but I have been down and dirty in the martial arts world, training with people who I don't think I would trade for anyone else. I have acheived many accolades already in various fighting circuits and plan on breaking into the MMA scene after college. Also with the Kickboxing I think the biggest advantage is having proficient strikes from varying ranges more so than boxing. Of course the best answer is to mix up ground and striking skills, but if you are a beginner with no prior training and want to become a tougher fighter faster, take my advice.
-Joe