I would have to say boxing or kickboxing, only difference is stance and kickboxing adds kicks, obviously. Now if you mean pure street fight where two guys brawl it out I would suggest boxing. If its more like the "organized" street fights like the wannabe kids who do "MMA" fights and put them on youtube I would suggest kickboxing but then if its classic then kicks are not usually liked so again choose boxing.
Remember its how good you are with the art and how much your practice and so forth. Plus boxing is fun.
Also if you think there is the slightest chance you will get taken to the ground I would suggest learning some basic wrestling.