My opinion, for what it's worth...

Go with the One Pass (CO) program, this will allow several things:

1) Earn mileage on NW flights
2) Earn mileage on HP flights
3) Allow transfer of AMEX Membership Reward
miles to the account
4) Should easily earn Gold Elite status in
OnePass which will allow CO/NW/HP upgrades

The WorldPerks VISA miles can be used to book a Continental flight, if necessary...but you might want to consider a new VISA with OnePass affiliation so the miles can be credited directly to the OnePass account for easier tracking and usage. Since most of the flying will be to OAK, which NW does not serve, earning the mileage in the FlightFund program doesn't serve you well if you do actually end up on a NW flight from time-to-time... the CO program will offer you the best of both worlds.