The athleticism and energy of Serena Williams is unmatched. She recently won the U.S. Open for the 18th time and there are no indications of her slowing down. She is well on her way to setting a record of the most wins of the U.S. Open competition. She should be automatically be entered in the tennis hall fame with the title of the "Grandest Player Ever".
She is a really great tennis player, but not knowing her stats and others stats I can't really make a good argument here. If she is, I'm sure someone will come along eventually that will be either just as great, or better. There is almost always someone talented enough to take someone's place in just about everything.
Serena Williams won her 18th title most recently. She has more major titles in singles, mixed or doubles amongst active players, both male or female. She has won 7 more titles than her closest US counterpart who have 11 titles to her name. She is a outstanding player for her nation.
No doubt Serena has had an outstanding career. 18 grand slam titles, that is fantastic! I am a literalist though, meaning that my opinions often seem cynical, but I just see the bare truth. In my view Sampras was the greatest American tennis player ever. He didn't win as many titles nor did he play as long, but his competition was much fiercer and he played with poise. If both of these players competed against each other in their prime, Serena would have no chance against Pete, meaning that he was the greatest American tennis player.
Serena Williams is not the Best ever. Records are made, broken -- come and go. While Serena is a highly valuable player, there will be someone who will come along one day and beat her records. This is the way it always happens as the tennis world is extremely competitive.