I'm pretty against putting bettas with anything. They're solitary fish. Many of the "stress" from bigger tanks can be caused by tank mates. A 20 gallon long, with a very gentle sponge filter, live plants, and almond leaves would be paradise for a male betta and would mimic very closely a natural habitat.
Who am I? Well I am a Junior Member of the International Betta Congress and a breeder of white HMPKs, red dragon HMPKs, black/red dragon HMPKs, metallic multi HMPKs, blue masked HMPKs, and now multi color HMs. Soon to add black HMs. I will be showing in New Breeder class in fall of 2012.