I've found the more room they have, the more active, curious, inquisitive they are. I put lots of plants, caves and hidey places in my betta tanks and they are always swimming around and going in and out of their hidey holes. There are ways to slow down a filter current too if your betta is bothered by it. I've used this method, very simple and easy and works great for my tanks.

http://www.petfish.net/currentkill.htm