Luigi is far superior for several reasons, one of
them being that he is green. Green is a far
superior color to red, because green clams people,
whereas red angers them. When people are playing
as Mario, it happens to be that they have deeper
'gamer rage' than while playing Luigi, because
Luigi calms the gamer more so than Mario. Less
Gamer Rage= happier gamers, which leads to a
better overall mood in the gaming community.
Second, Mario is a cruel brother. Mario uses Luigi
in order to save princess Peach, but in the end
Luigi never gets the girl. Mario doesn't even
help Luigi to find a girlfriend, and that's
downright mean.
Finally, Luigi doesn't advocate obesity. Luigi is
portrayed as the tall, healthy brother. Mario is
the short, slightly overweight brother. Kids
playing as Mario want to be like him at a young
age, and then over eat to look like him. Luigi
helps kids portray a better body image than
Mario.
It's obvious that Luigi is the better brother.

I see Mario as a positive role model for children.
His less than perfect physique shows kids that you
don't have to be skinny to be the hero, like oh so
many Disney movies seem to contradict (will
someone please get that chick from Hercules a damn
sandwich. Seriously).

Research has shown that human's bodies have
individual set rates for body size and shape.
Basically, everyone's BMI is different.
Additionally, BMI has been shown to be an
extremely poor indicator of health, and that in
reality, it plausible to be 'obese' and physically
fit.

Mario embodies this sort of idea and leads
children to accept who they are. Mario is
physically active (all that jumping) and eats
healthy (plenty of mushrooms) and this encourages
children to be their best at any size.

Luigi , on the other hand, may lead children to
adopt health-damaging fad diets in order to become
skinny.