Whoever has learned to do it properly. I would imagine men have an advantage as a beginner. But a woman who pays attention to what a man likes or not, will be good too.
Both are great. Women because it’s sexy sensual, and guys because it’s easy to get, and some are really, really good at it and want nothing more than to get you off.
On average, men. But some women are perfectly capable of giving as great a BJ as you would get from the most skilled male cocksuckers. But some women only do it out of obligation, and so, they are the ones who drag down the average for females. It’s not fun for them, so it’s not anywhere near as good.