AF has better food, KL has nicer crew, AF has 1-2-1 seating, KL's (current) 2-2-2 seats are more comfortable but less private. That said by next January all KL's 777s should be retrofitted with a new 1-2-1 product that is functionally identical to AF's.

KL gives you a huisje, AF has you connect in CDG.