As far as I know; Bettas, regardless of type, all carry the same temperament. Sex does make a difference as females are SLIGHTLY less aggressive towards one another, but they can still be a ticking time bomb if you've got multiple females in a tank.
One of the more experienced people can confirm or reject this, but this is true as far as I know.
I believe that there are a few of us who would almost put males together before trying females in the same tank again. I had females in the same tank and one of them killed not only the other betta females with her but every fish I tried to put in with her. Another member had put some very young females together and they attacked each other and injured each other and even attacked her when she went to separate them. A third member had a similar experience. My males that I have in my 25 gallon tank with a very clear Plexiglas divider are quite peaceful toward each other, no flaring or posturing and even do not spend much time watching each other. They go about their business in other parts of the tank and play on their own and seem to spend more time with the loaches and otos that share the side of the tank with them and love to find little places to explore.
Yup, I think Lava and Phlox would have gotten along better than my girls did. Also, everything you read says females are less aggressive than males and therefore good to put in community tanks. These people have obviously never met MY ladies! I wanted to get Otos for algae cleanup in their tanks but they are so aggressive they would kill them! I bought a snail for Aenara's tank (she is my LEAST aggressive female) and she killed it within minutes!
IMO, Bettas are truly best all alone. They enjoy human contact and are gentle and playful with us, but it goes against their very nature to share a tank with other fish. Many people have successfully kept Bettas with Otos and Cories but there is no guarantee. Crowntails and Cambodians are generally considered more aggressive than Veiltails but really every Betta is different. Both my males are Crowntails and very gentle (one is now passed away). My females will kill anything you put in the tank but are very sweet on their own and get along nicely in divided tanks as long as they have their own territory and no other fish invades it. The thought that my females would be good community fish is laughable!
Females are more aggressive than males, without a doubt. At the advice of the 'fish expert' at petco, we tried 4 girls in 1 tank - DISASTER! Despite what they tell you, the females can't be together and this misinformation might stem from the fact that very young female bettas are raised in big tanks together.
Just to solidify these points; at my local Super Pet they sell their females from a community tank, full of female bettas. The last time I saw it, ATLEAST 80% of them were flaring/chasing each other around, 10% or so were going about their business without a care, and the other 10% were dead/wounded.
Do not under ANY circumstance, listen to what people at pet stores say about bettas living together.
Also, if you do intend on putting them into a community tank, be absolutely sure you have fish that will be able to live together. Fish with large fins, guppies for example, can cause issues. Other aggressive/semi-aggressive fish will likely not work as well either. "Fin-nippers" are no good either.
Bettas can be quite difficult to find tank mates for, sticking with bottom-dwellers may be the best course of action if you want extra fish.
At one of the pet stores arount here too, they put all the females in one tank together. On one hand, it makes me happy to see them out of the little cups, but on the other hand they're all fighting. It's too bad they can't put one per tank or something.
I've been lucky with my little Artemis in that she has a very good temperment. When I first put her into my community tank with my Cardinals, I watched her for a bit. She initially started to go after a lone Cardinal, but as soon as she saw that there were more of them than there were of her, she backed off. In the three weeks I've had her, she and the cardinals have been very good to each other, all going their separate ways around the tank. I just got lucky I guess. She doesn't need to know that they're not agressive.
It all comes down to the individual betta's personality. I try to find the passive ones because they ultimately go into community tanks (but only one betta per tank). Fortunately I haven't had a problem so far, they've all done well with their respective tankmates. Lets hope it stays that way ;D
We've heard stories of female Bettas that refuse to get along with tankmates, but it's nice to know some do like Artemis and our friend's little Cleo who got our Sora's cory cats when we had to find them a home. She sleeps and swims with them. I'm hoping Angel will be like that because we want to give her a couple of otos for tankmates.
I've not seen a place have all of the females in 1 tank, but that's as bad as the little cups I think.. you end up with a lot of stressed or dead bettas either way.