My daughter has mollies. I got her 6 for a 20 gallon in her room and expected at least a few to die... she's 10 and this was her first solo tank, she feeds them, cleans them (with some supervision) and does water changes. So out of the six we got I thought she might end up with 2 or 3... Nope! All 6 are thriving and while they're still little now, I know I'll have to get another tank.. >.<
She has 4 normal dalmatian mollies (3 girls and a boy).. we call them "the puppies", because they really don't have personalities, they just like chasing fingers. Honestly I haven't found any personality to any of them.. they're kind of fun to watch interacting with each other and the tank, but they're not nearly as intriguing as a betta.
She also has 2 sail-fin mollies, a little black marble male and a HUGE white female. The female is so sweet but a little pushy. She watches my daughter do her homework.. just floats there by the glass watching, even when no one is interacting with her. The male probably has the most personality of them all. He sleeps in a cave, keeps the other fish in line, jumps for his food and follows fingers, but still... not even half as much fun as a betta, at least in my opinion.
I'd go with a sorority.. I LOVE mine. The girls are so much fun, they interact with each other and I spend a lot of time just watching them. They've each developed personalities, like Rosie who has an obsession with checking every single inch of the decorations for.. er.. something, and Princess who thinks she's in charge (when Tidbit isn't around) even though she's the smallest. By far, this is my favorite tank to watch.