Re: Martina Navratilova VS Serena Williams
I think peak Martina could beat peak Serena, and vice versa. Remember playing a serve-volley game in this day and age and with 2002-2003's physical capabilities with 2008-2011 mental capabilities of Serena completing the player at a hypothetical peak, Serena could cut all or most of Martina's time once she got a handle on the serve. Martina was good at making incredible volleys, but many players of this generation (Serena included) would love the target at net, even if Martina was doing at least 50/50 (which at her peak with the aid of technology advances and fitness advances, would probably do better).
On a grass court, no doubt Martina. Clay would also probably favor Martina, but her groundstrokes aren't very powerful and Serena could eat a lot of those up because clay could afford her more time to set up and the slice would bounce up a bit more. On a slower hard court, it would probably be Serena, and on a faster hard court, it would be 50/50.
Tennis's Silver Millennium
Queen Serenity (22), Neo Queen Serenity (Sailor Garbi) (RG '16), Sailor Venus (7), Sailor GOATra (2), Sailor Kerber (2), Sailor Darth Vika (2)
Sailor St. Kim (4), Sailor Mahree (2), Sailor Anci ('08 RG), Sailor Seles (9), Sailor Dokic, Sailor Testud, Sailor Zheng
King Stanimal (3), Shittennou: Gasquet, Djokovic (12), Murray (3), Lajovic, Thiem, Sock, Cuevas