I think that we can't compare ATP and WTA tennis. They are very different, so I prefer to enjoy both. The are almost the same rules, of course that ATP players are from far better than WTA players if we put them on a same match. In this topic I think that there is no debate to do.
About the war of ATP vs Williams, I recommend to read this article (it's in spanish, so use a translator). It contains the opinion of Ferrer, Toni Nadal, Carlos Moya, Galo Blanco (Milos Raonic coach), etc. http://www.puntodebreak.com/2012/10/...-100-masculino
The key problem that they enfasize is the mobility on court more than just the serve or the power.