I know I can count on Schmuck not to bother gathering any evidence to the contrary, but I won't sink to his standard, fair reader. Here are the reasons, based on actual facts, to bet on the younger sister.
The last time they were both fit and fully committed to tennis (2002-2003), Serena was clearly the better player. She won five of the eight Grand Slams played in those two seasons and beat Venus in each of the five finals.
She had a more versatile, consistent serve and more reliable ground strokes than her sister.
I know, I know. Venus beat Serena the last time they played at Flushing Meadows in 2005. But injuries had reduced Serena to a part-timer at that point. She played only 28 singles matches that year compared with 47 for Venus. Serena played even fewer - 16 singles matches - in 2006.
So she's just now getting back to the kind of schedule (36-6 this year) she played when she was the unchallenged queen of tennis. As she started to work her way back last year, Justine Henin, not Venus, was her arch-nemesis. Henin is retired.
Venus' career renaissance has occurred mostly at Wimbledon, where she has won the past two years and beat Serena in July. Hard courts are different, and Venus hasn't won a Grand Slam on one since 2001. Five of Serena's eight Grand Slam wins have come on hard courts.
Serena has lost serve only once at this year's Open and has rolled through each of her matches in short order. She's playing on her best surface and is fit and healthy for the first time in five years. If she was the better Williams before her body betrayed her, what makes anyone think she won't be now?