Mario vs Luigi
Alright this is the question that I know has been on everyone's mind since they first came out with the first Mario Bros. game wayyy back in the day. I have a theory that one day Luigi will one day just snap and attack Mario. The reason for this outburst would most likely be because Luigi is jealous of the fame that Mario gets and he hates being known as "Mario's brother." Making that my argument for the reason why, let us get to the theoretical fight and the advantages and disadvantages of the fighters. Luigi's obvious advantage is the fact that he's taller and seems to be slimmer than Mario. This would give him the reach advantage and would be great if he could keep him at a distance. Mario, though, is the brains of the operation and, despite the disadvantage in height, once he gets inside of Luigi's reach he could cause some trouble. His stoutness gives him a lower center of gravity and he could take him down and put him in and arm bar or just punch away at him until he has nothing left. Overall, I would have to give the fight to Mario, but the issue is still up to debate.