I have had two female bettas for 3 years and have found that they are extremely aggressive. I made the mistake of putting them, at first, in the same bowl since the person at the pet shop said two females together would be fine. Big mistake! I woke up to actually hear the two fighting and immediately took one of them out and they now live happily in separate bowls. They are extremely beautiful and are my favorite fish - even with the attitude.
I have a male betta that shares a 110 L tank with a female orange gouramie and a common pleco, and there has been no aggression towards each other. I then introduced 3 female bettas and within 3 days the male betta pecked of their tail fins. He then started to hide and did not look very happy. I decided to separate the females, they now live in a 55 L tank the females recovered very well and every one is happy.
I have 3 male bettas, one is a veiltail (mutt lol), the other two are half moons, all red. The half moons are extended reds. They are a great fish, even the selectively bred types. If you can handle it, they do just fine in 2 liter bowls, but you must change their water every day with aged tapwater that has been dechlorinated. A little salt every now and then seems to help, but if your fish is healthy overall you won't need it. The food should be a little flake (just a few 2x a day) with the occasional brine shrimp meal. Only feed live foods when you're going to breed them. I wish people would look beyond the veiltail variety you can find anywhere, and purchase the other tail types, they are much healthier. A hefty investment of $50 for a good specimen, but you will say it's a good 2-3 year investment if you know the basics for of caring for fish.
I have a male Betta in a 200 L community tank. Early on my baby angels made a feast of his fins, but all that has now stopped. I have three largish clown loaches with whom Simon (the betta) seems to stalk the minute they come out of their cave. I have noticed that two of the loaches are now sticking up for themselves and barge him back when he gets too aggressive. As far as the other tank mates go, Simon is fine.
I have owned a male Betta in an 11 L filtered tank for 2 years now. About a year ago, I decided that it was a rather large tank for one fish, so I went to the local fish store just in search of a small peaceful fish. I decided on a single male Cherry Barb. I slowly introduced him to the tank, the Betta took immediate interest and slowly approached him, he didn't act aggressive at all, but almost playful. I figured since the Betta was the king of the tank for a year he would try to exert dominance over the new guy, but instead, to this day they share the tank without the slightest problem. Since then I have also gotten a small Apple Snail, neither fish bother it and obviously he is to slow to bother the fish. I have heard that a lot of the time when a Betta is kept with one o more fish they become kind of docile and lazy. Not this guy, he is almost constantly swimming around puffing at his reflection and just acting like he did for the year prior to the new tank mate's arrival. The only difference is he keeps his bubble nest in one part of the tank instead of the entire tank. I love sitting back and watching my beautiful fish. I hope if you are thinking of introducing new fish in with your Betta that this was helpful in making your decision. Just remmember that the Betta seems happier with a smaller, non-aggressive fish.
This is my second betta and I have had him for a year. My first lived about 3 years in my dorm room. My betta loves to eat from my hand. He will come right up to my finger and I will give him a minuscule piece of chicken or fish. If I hold it right above the surface, he will jump and try to get it, most times very successfully. Of course, I have to change the water more frequently because he is eating different than most fish. My guests who are used to those skittish fish are amazed at this guy. He will almost attack the food from my finger. He even attacks his fish food the same way floating on the surface. He loves it when I come into the kitchen (he's on the counter) As soon as he sees me, he's like a little puppy. He starts swimming back and forth really fast and looking at me. We have a signal for food. I wave my hand slowly in front of him and he will even wake up and start swimming around fast waiting for me to feed him. Both of my bettas were hand fed this way, but I will say that this one definitely has more personality.