Of all time - Moriah Jefferson and it's not even close. On this team - Aubrey
MoJeff was MoJet. She was the fastest down the floor--think the South Carolina game when she blew by 9 other players from basket to basket. She also came up with seemingly every loose ball on the floor. She is quick as heck and one of the fastest player in the WNBA, possibly THE fastest.
On the current team, here is some actual data: Early last season, Paige was bragging that she was the fastest player on the team, consistently winning the sprints. This is true. But Geno pointed out that Aubrey and Mir--both of whom were track athletes in high school--were injured and not participating. They were the 2 fastest. I don't recall if Aubs was faster or Mir was faster, but they beat Paige and everyone else. Unless her back issues slowed her down, Aubrey is clearly the fastest on the team. Watch her on the fast break--it's fairly obvious.