From AMS, it makes sense to fly KLM/SkyTeam. The question is to which FF program you should credit these flights.

AS has it advantages and fans, but gives almost no benefits when you fly DL/KLM/AF. You can theoretically can get DL free domestic upgrades, but you're at the very bottom of the list and it will happen so rarely that we might as well say never.

It sounds like your travel pattern is enough to earn GM (Gold) on DL, which means SkyTeam ElitePlus with lots of perks, including SkyPriority and lounge access. I suspect that the same is true for FB, but you need to check earnings for your particular fare classes as this can differ a lot between SM and FB. Look also at the changes to DL RDM earnings starting in January. It's much easier, and sometimes cheaper, to get EC seats on KLM with KLM status or on DL with DL status. DL miles aren't very good for KLM/AF business class award tickets (and cannot be used for FC on AF) but FB miles aren't very good for DL award availability either. Either way, you will pay YQ fees on award tickets originating in Europe.

BTW, DL does do status challenges, but not outright matches except possibly as part of a corporate contract.