I voted corns, though it was a tie between them and kings.
I have two corns (one I just picked up, the other I've had for 9 months) and they are fabulous eaters. My older corn has literally skipped a feeding one time, and that's when he was in shed. I love all the morphs available too. Plus, I don't have a preference for them in terms of keeping them: they do great in both a tank and a tub.
Kings: I have a Cali right now, and he has been a great feeder for me too up until about a month and a half ago when he went off feed for the season. But they are still usually great feeders and do well in both a tank or a tub. The musking isn't even that bad either, plus I love king's little "mad" faces, they always look grumpy. :P
For both though: I hope your mom doesn't mind FAST snakes over the beefy "lazy" ones because whew, corns and kings can fly when they want and sometimes their speed can be a little intimidating for those who are a little hesitant around snakes (which I'm only ASSuming your mom is if she didn't like the balls because of their girth).