One of the highlights is that it is very decorative. Square braid is what I usually recommend. It is much sturdier but not as decorative. The candles do seem to burn more evenly with the square braid. Lead core was used in the past, but by common consent US candle makers do not use it.
Some candles made in other countries still do.
Paper core is also used in container candles. It does tend to smoke more than the metal core, but it is an option for people who do not feel comfortable with the metal. Stearic acid or sterine is an animal or vegetable fat byproduct. It is used to and make the candle burn longer. I have also found that the color fades faster with the stearic acid than with the other additives.