I tried butter once, just for the novelty of it. It felt too heavy in the mouth to do regularly. I also got tired of the flavor in my mouth for that long, even though I like the taste of butter on food. As to swallowing it, if you are concerned with cholesterol, maybe that isn't a good idea. Also, unless the butter is organic, animal fat stores toxins, so you could be introducing more toxins to your own system.
In my early days of oil pulling -- last year -- I also used canola oil for a while, regular grocery store type. It was just as effective in whitening my teeth and keeping my skin clear. However, fellow posters here warned me that its use is controversial for a number of reasons, something I didn't know before, so I quit using it.
I agree with you that any food-grade oil would be effective for pulling. The reason for using the best quality is because of the theory that nutrients and other substances in the oil are absorbed by the mouth tissue.