the westin business center routes the majority of telecommunications in the northwest i believe, which puts them as a very rich peering point.
companies like sextracker (fci) host there for instance, and have a multi-gigabit network internal to the building. at least, that was the way it was 3-4 years ago, i can imagine it's only larger.
SF bay area would have the advantage of being close to PAIX... it's probably pretty fair. especially if you're only getting a dedicated server or two, you won't notice much difference. if you were going to be buying multiple FE's or some gigE, it could make some difference then.