Gotta disagree. Serena's resume is much longer than Venus', yes. Serena's dominance was sustained over a longer period of time, yes.
But take both players at their peak performance levels, and nobody in history is beating a Venus Williams at her best.
[NOTE* Both Venus and Serena have been set back by major injuries and personal life traumas, and Serena has been able to bounce back fairly often and keep up her performance at close to her peak. So she has the results to show for that. There's a lot to be said for personal resilience. And both Venus and Serena are far ahead of everybody else.]
When Venus was on she couldn't be beat. I admit that's a personal opinion. But I liked her approach to the game. Every time she swung the racket, every shot, she was looking to hit a winner. In those 2 years of her peak, the only way Venus could lose is if she beat herself with unforced errors. Venus still has the record for fastest serve in history. The power of her ground-strokes was unmatched, tho Serena's came close (Serena's serve was also close, but no cigar). Venus's court coverage was also unmatched, she was fast as hell, and her length further allowed her to get to every ball. It is Venus who taught everybody, both men and women players, about the swinging forehand volley. That used to be a tennis no-no.
Serena is the GOAT, I admit. The resume of sustained excellence is too long. But there is a coffee-shop argument for Venus being the better player.