I've read GloFish come from nippy stock (Danios, it looks like) and might not be good friends for bettas. YMMV of course, and I don't have any personal experience with them other than admiring their striking colors at the store.
Tetras seem to work out well. I have 11 girls in my sorority, and 11 tetras (neons and glowlines) in with them. The girls steal the micro pellets I feed the tetras, and the biggest of the tetras boldly steal betta pellets if the girls aren't fast enough.
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