It all depends on what type of fish you want to keep with him. But to be honest male fighters do best in a tank on their own. I have four which all have their own 5g tanks and they are perfectly fine. One of the males has a couple of ottos in his tank and he doesn't bother them.
Hi
Well I have to say, I have a fighter in a community tank, and he has no problems with any of the other fish, he just does his own thing and sits at the front of the tank 'wagging' his tail looking for attention. I think you just have to be careful which fish you decide to choose to keep with them and not have territorial species that may offend
they can mix ok with other fish but they are all individuals so people will vary on what they say.
I would say avoid adding a betta to a tank with anything prone to fin nipping and also to a tank with anything that looks vaguely like a betta such as something with flowing finage like a male guppy. Also mine used to have a go at anything that swam near the surface, eg gouramis and hatchet fish.
Adding a betta can be the fastest route to getting a second tank and then you are well on the way to multiple tank syndrome - BEWARE.
DD