I have never owned either, I just never got "into" herps through the same typical means as others either. Yet, after keeping and being around snakes of sorts, I strongly will suggest corns over balls hands-down everytime. Who would not though, right? Maybe it is the newer persons personality that makes them think that corns are boring and balls are cool, who knows. Being that most new herp owners do it to be cool, fit in or simply be a bit different for obvious or not-so-obvious reasons. Not many folks started into herps in a natural interest of species they grew up around, or else I think many new herpers would be into Thamnophis, Lampropeltis, Pituophis, Nerodia and the like. Not many are. Look how many start off with Bearded Dragons, Leo Geckos, Balls Pythons and so on.
Out of the many (to many) ball python owners out there, I do not see why they have become so popular with new snake owners. I hear just as many ball python problems with new owners just as much as new iguana owners these days. Not that they are not a pretty snake, because EVERY snake is, just that there are way to many reasons I personally believe they make a horrible first snake over several other great species that are overlooked, especially for a boid. I also think it has to do with the fact that they are "cool" to new snake owners and those new to herps in general. Snakes like Thamnophis, Corns and the like are just looked at as stupid, ugly, weak things that do not get other peoples attention like a Python! does. Get what I am saying......?
Corns make good first snakes, simply due to the ease and appeal of husbandry and their demeanor. In general, they are just a very simple snake that makes getting use to the care of snakes a breeze. They of course are not the only snake that fits this bill, but one that is reasonably and easily available to most folks. Nothing is better to start with than something extremely easy and hardy. I think a lot of folks think this makes them look dumb or weak to others, so they just must start with something a bit stronger or cooler. Thus is a common reason I hear from new snake owners.
I also see that most new herp folks want to just jump into herps in general like they are natural born herpetoculturists or herpetologists, and want to be Ralph Davis or Bob Clark after only keeping 2 snakes for a time of 4 months. They sit back and read some pages from these (and other) forums, read some Reptile magazine and have friends that are "reptile experts," so they just have to be as well. Many have not taken any serious time to research anything like they trult should. They cannot admit they are new and should just sit back a few years and gain some true experience with reptiles. How many have actually taken time to go herping? It is rare for any to know what animals live in and around their homes even, but they want to start with an animal that gives even experienced folks trouble? Seems a bit odd to say the least...
Not every new herper is the same. I know several that started off with species that almost every new herp owner has never heard of. Not every beginner ball python owner is going to have bad luck, and not every beginner corn owner is going to have the perfect snake. That is just how it is, but generally I see it the way as I have described.