In answer to your question, you want them to burn as clean as possible, consuming as much of itself as possible. That would be my answer. So, for containers, you want a clean burn with no hang up, or very little (some people like a little hang up feeling that is safer), and as little smoking/sooting as possible. If it is scented, you want a nice throw on top of that. Now - producing a candle with those characteristics... oh the testing that ensues. Welcome to the forum.