Most people agree the AMS is a better airport to connect at. Though with a long enough layover, CDG is doable. The main advantage to CDG would be the option of a true Premium Economy product to chose from between DL and AF. KLM Y+ won't be a whole lot different than DL C+ and there's no MQM bonus. Premium Select on DL gets a 50% MQM bonus, and I would assume this is true as well on the AF metal equivalent if you book it on delta.com with a DL flight number.