Serena vs Venus? Who's better tennis player?

Jim from Florida is curious what you think who is the more accomplished tennis player, Serena or Venus? He gives slight advantage to Serena saying that she has more powerful shots than Venus. And there is also the fact that Serena has edge in their head-to-head encounters.

I personally believe that Williams sisters play almost exact style, and it is really a question of who has the better day on court rather than who's more accomplished player. Serena Maybe has the small edge but there were very few convincing victories from both sides. Current form and few lucky shots are things that decide winner between those two. After all they had the same teacher, practiced together, so they know all about each other. That's why their matches are always unpredictable.

What's your opinion? Is Serena really better and more accomplished tennis player than Venus?

Serena or Venus - Who's better and more accomplished tennis player?