Yes, there is kind of a rivalry between SF and Seattle, one that the Seattleites do not want to acknowledge (also maybe because Seattle is much more peripheral and provincial).
But the number of people that appreciate the quality and the potential of the northern location is continuously increasing, or the number of people that consider moving here. Yes, difficult not to notice, given that the number of cranes in Seattle is the same as SFO, Chicago & NY combined ;)
Here comes a new article from the Economist that provides a different view: the 2 hubs are actually converging, because of the exchange of capital, brainware and people.
There are 25+ flights daily between SFO and SEA, 10+ between SEA and SJC, 10 between Oakland and SEA. Can you figure how many people daily that means?