Finnair.com may just have the best MMB (Manage My Booking) interface for oneworld carriers.

For example, I recently redeemed almost all my remaining BA miles for a single-partner award on CX/KA. Naturally, the booking used my (no-status) BA FF number, and there's no way to change it to my AA (Emerald) number on ba.com -- I think a phone call is required to do this. But, it takes maybe 10 seconds to easily do this on finnair.com. Seat selection for the CX/KA segments? Maybe another 30 seconds -- easier and quicker than using the CX interface. Update an old home phone number that carried over from ba.com? Just a few more keystrokes.

Another example was a recently-booked OW130C, using my AA miles. Changing seats on the AY, MA, BA, and IB segments? It couldn't be easier.

As you might expect, the only thing I couldn't do on finnair.com is change seats on the AA segments.