Re: Which #1 can have the most LONGEVITY?
If Safina gets to number 1 anytime this year she will hold on to that spot almost certainly until at least Berlin next year. The reason? She has very few points to defend between now and Berlin next year. She is almost sure to simply add to her current point total, notably at the Australian Open. That said I'm not sure whether Safina will be able to sustain a number one ranking over the next summer when she does start to feel the pressure of defending this spring and summers points.
Honestly I don't think there is a single player in the game right now who looks like they are going to be able to break away from the pack, so from next summer onwards I expect the number 1 ranking to continue to change hands quite frequently.