I think it depends on your personal experiences with each species.
For me Ball Pythons have been wonderful easy going additions to my house. They are calm, great for handling, feeding problems are easily over come or understood and they take less maintanence IMHO than a corn when it comes to cleaning.
Corns are more prone to eat with no trouble, will take mice forever, and rarely bite. But as youngsters can be so fast and whippy, they take a bit more cleaning etc.
Frankly I think MANY species are just fine for beginners. It's not so much which snake is the best starter, but which type of person is the best to own a snake, and that means researching fully whatever species you are interested in....first snake or no.