I've got to disagree. The OP has stated that longhaul travel will be in J in any case. Unless the OP has a current ATP and 777 type rating, there's no CO upgrade in their future!
AA codeshares with JL ex-NRT extensively, you might call it a gimmick, I call it a chance to fly superior airlines
And if the OP can get to YVR, They can leverage CX to Asia and BA to Heathrow. Short hops down the coast also open up the JL and CX flights to Asia (BR is more limited unless TPE is your destination, in which case I believe there's an SEA-TPE nonstop which is nice).
AA also provides much easier mileage redemption IME, not to mention the EXP desk (fantastic!) and 8 eVIPs for upgrades on AA metal, nice for upgrading to F (where's F on CO?). And you still get the domestic upgrades.
Now, if CO is directly serving your European destination and you are travelling enough that you want to knock off a leg, then that's an advantage to CO. But if you are going to end up using KL's network ex-AMS, then I think you'd be better served by using BA's network ex-LHR. At least BA still offers business class on their European network, as compared to the "nicer service in coach seating" that KL calls "Europe Select."
Oh, did I mention that at least if you have time to kill at ORD or LAX on the international trips (and soon to be JFK) you'll also have the Flagship Lounge (which is, whilst not CX's lounge in HKG, is far beyond any regular KL/CO/NW lounge).
And if you can take the short trip down the coast to LAX, you've got that ability to upgrade to F LAX-LHR again...
Steve