I have lived in both Portland and San Francisco, and have spent some time up in Seattle. They are all really great cities, however, at your age, in your situation, I would probably prefer San Francisco or Seattle.
Particularly, in regards to starting a business, I found the people in both San Francisco and Seattle to be much more motivated than Portlanders. Additionally, both of those cities have larger pools of qualified candidates. From what I have heard from my boss who started her own small business, Seattle is a decent climate to start a business, whereas California can be nightmarish, due to a plethora of regulations and exorbitant fees, and Portland is tougher as well. However, as someone mentioned previously, the possibility for obtaining venture capital support etc. is good in the Bay Area.
I do not know much about the running scene in Seattle, but when I explored the possibility of moving there, it looked pretty good, with some good routes in the city, trails nearby and a decent club scene. I personally did find San Francisco to be far superior to Portland. There is a more diverse variety of areas to run, more races, a solid club scene:
http://www.pausatf.org/
, and better and more challenging trails within a short drive. I also prefer running in areas that are more open with changing views versus being tucked into trees, like Forest Park, for an entire run. However, many of my Portland friends are perfectly happy doing the bulk of their running buried among the Douglas Firs. It is a personal preference.
I also preferred the year-round weather in San Francisco. The summer's in Portland are, no doubt, fantastic, but the constant gloom and wet in the spring, winter and fall can get old. That is why when I relocated I picked San Francisco over Seattle. I was ready for a little more sun and less rain. Even with the foggy summer days, you still get a lot more sun in the city, versus the Pacific NW, and many of the outlying areas are constantly sunny.
With all of that said, at this point in my life, nearing 40, married and settled in a career, with some family and friends still in Portland, I would choose to go back there versus San Francisco and actually have thought about returning recently. That is mostly attributable to cost-of-living and no longer wanting to deal with how incredibly busy and dirty everything is in the Bay Area. However, I am very happy in Colorado for now.
They are all great cities and regardless of what you choose, you are likely to have a positive experience. Good luck!