There are four .32 revolver cartridges: .32 Short, .32 S&W Long, .32 H&R Magnum, and the newest, .327 Federal Magnum. That order is also from least to most powerful. I believe (Someone will likely come along to correct me if I'm wrong) that the Taurus 731 is chambered for .32 H&R Magnum.
.32 doesn't leave a very big hole for a self defense gun, and ammo can be tough to find and more expensive. For a carry revolver, IMHO, the best choice would be a Ruger revolver, wither the LCR or SP101, in .38 or .357 Magnum. While a Ruger will cost you more than a Taurus, it won't be by a whole lot, and the better quality will be 100% worth it if this is a gun you plan to trust your life to.