Man this is a well worn topic...You'd have to be a little more specific...For instance: How would a boxer fare vs a TKD w/TKD rules or how would a boxer fare against a Muay Thai fighter in a real world street fight? It is pretty safe presumption that comparing a boxer and a traditional martial artist of equal time training and over all athleticism the boxer is going to have better hand speed, accuracy , technique and power. He is also going to be better at not getting hit. That being said boxers have not faired very well in kickboxing...A good MT leg kick is a great neutralizer to a boxers superior hands...It slows their footwork and by weaking their stance sapps their power....It is also a good setup for high kicks....that being said the best defense to a nasty leg kick is to use one yourself, and its not something that would take an enormous amount of time to get proficient at. Kicks run a certain level of risk though. If you miss or its caught you could easily end up on your ass. If I were to train in just one striking discipline it would be Muay Thai. Its geared towards close in fighting and the utilization of knees and elbows..so IMHO in a street fight a boxer is going to be more succesful against a traditional martial artist due to the simple fact that boxers spar all the time and all be it limited, my experience with traditional martial arts is that they don't "fight". It is hard to implement a technique in the chaos of a real fight if you've never done it at full speed against a live target thats returning the favor.