Your milage may vary, but experience in suitable tankmates for a betta as of late:
Betta w/ female betta - as the betta never built a bubble nest, he pretty much left her alone
Betta w/ 2 male guppies - chased them around for maybe 2 minutes, then got bored, nothing else ever happened
Betta w/ dwarf gourami - they outright ignored each other
Betta w/ 3-spot gourami - After about 30 seconds, it was decided they were going to go at one another, so the betta was removed
Betta w/ rainbow shark - You'd never think of the weird combos, and they ignored each other for over a year. And then one day, the betta started pestering the shark for a good 10 minutes, until the shark grabbed him and slammed him against a rock..
Anyways, just for some first hand experience... won't even bother mentioning the betta w/ 6in long crayfish, that one is kindof a given....
Betta w/ female betta - as the betta never built a bubble nest, he pretty much left her alone
Betta w/ 2 male guppies - chased them around for maybe 2 minutes, then got bored, nothing else ever happened
Betta w/ dwarf gourami - they outright ignored each other
Betta w/ 3-spot gourami - After about 30 seconds, it was decided they were going to go at one another, so the betta was removed
Betta w/ rainbow shark - You'd never think of the weird combos, and they ignored each other for over a year. And then one day, the betta started pestering the shark for a good 10 minutes, until the shark grabbed him and slammed him against a rock..
Anyways, just for some first hand experience... won't even bother mentioning the betta w/ 6in long crayfish, that one is kindof a given....