Are you after only points or elite status and upgrade?
If you're going only after points, I'd suggest Alaska Mileage Plan. They're partners with American, Delta, Northwest, and Continental. You've almost covered. Then open either a UA os US account for your Star Alliance flights.
If you're after status and upgrades, you need to look at where you're going to fly most.
Personally for business travel, my most important requirement is nonstop. Then I'll worry about points. Your time is very valuable.