When I got my tank for my desk, knowing a lot less about bettas then, and having not yet discovered this forum...
I bought the 2.5 G "Betta Bow" which is a divided tank. Well, the divider is more like a flat plastic strainer, so while it allowed water to move nicely, the bettas had pretty much a clear view of each other.
I got two males, a red and white crowntail whose colors I loved (he turned out to be a marble and is now mostly blue and purple, but I love him even more because of it!) and a red/cellophane veiltail.
Two VERY opposite personalities. Red - very aggressive, patroled the divider, constantly flaring at Ghost, who honestly seemed to care less. Actually, I think he secretly did care...he had quietly figured out how to get extra food. He would drift up to the divider and just...look. No flaring, no gyrations. Just looking. And Red would take the bait, and come up and flare and swish around. And those food pellets he was too excited to eat would get skirled through the barrier, where Ghost *was* quick to snap them up.
The Boy Feesh: Indigo CT, Lavatail CT, Ghost CT, Chicory HM, Redfish VT, Magic DT
The Girl Feesh: Christmas CT, Shine VT, Snowflake CT, Stripes VT, Midnight CT, Grif VT, Tangerine VT, Wraith CT, Amethyst VT, Ice CT, Poe CT, Turquoise II CT