For me, I've always prefered the heavier-bodied snakes--I just seem to like their looks more. Plus, corns are pooping machines--they have such a higher metabolism (which keeps them skinnier than most pythons) than ball pythons that they digest much faster, so you spend much more time cleaning cages. On average, my ball pythons use the bathroom once per week, though sometimes they will hold it for two weeks (typically, I've noticed the females doing this more so than the males). Either way, you aren't having to spend nearly as much time cleaning cages with the heavier-bodied boids.
Otherwise, I agree completely with Rob (boggylizard) on all the other reasons. Like he said with corns, they can be a bit jumpier as babies, and is the main reason I would recommend a ball python as a first snake for a child. I would recommend either one for a teen or adult, though. Teens or adults might not be as frightened by the jumpiness some corns can have, so no issues with them getting too scared to continue properly caring for the animal.