I had a hard time deciding which was my first reason. (When I say first I mean maybe before you got 50, but the reason for getting your first couple or so...) My first betta was Jack, and I would have to be honest and say I probably got him because bettas are easy to take care of. He doesn't need a heater, and he doesn't need a big huge tank. Second choice, probably colors, they're so gorgeous. But what about personality? EEK! I made this too hard for myself even!
It was finnage and colour that made me buy my first one, but it was his personality (ok as well as his looks) that made me buy my second and third.
I can watch them for ages, and I love to feed them so I can watch them jump out of the water to get their food. Veeeeery coool fiiiiiisssh.
My favorite fish of all are cory cats; I have quite a few tanks of them. But the thing about corys is that they all live on the bottom of the tanks, so there is all this lovely space at the tops.
Bettas work out perfectly. They have lots of room for swimming, a few plants to swim through, caves to look into, and lots of little friends to keep them interested and amused.
I voted "pretty". I haven't been able to keep them in my smaller filtered tanks and they got sick, so they aren't that easy to care for, IMO. They can be kept in small spaces, but I don't like stuffing them even one into a dual hex.