What horse bit should I buy?

I already have a d-ring snaffle, but I got a new bridal so now I have a reason for a second bit. I would like to know what the most relaxed bit is. She goes best in just a halter, longest stride and more perky, so I was wondering what bit has the least resistance and is easiest on the mouth. I would go with a sidepull, but I cannot use it in shows.