SkyTeam - what skyteam milage programm to choose

Hello,
following problem . I normally fly united , but I will do some business class trips from Europe to Mexico this sommer (maybee 5 or so ) The client will use KLM/air france.
SO what is my best programm. Later use would be free tickets in business class or better with a decent availlablity. I have allready status with UA so status is not that important becuase we have business class ticket anyhow.....
I thought to put them into my delta or KLM account but the award availlability just sucks.....

Please share your 2 cents.
thanks
JR

Kl/AF has comparably good award availability and is quite good for Business on the earnimg side, too.