Years ago, 10% of luggage going through Amsterdam Airport was lost. Is that still true? We have a choice to fly through Paris or Amsterdam to Prague on Delta.
According to this article the rate of bags lost in Europe is about 8 per thousand. That's less than 1%.
It goes on to say that 85% of bags reported as missing are delivered within 48 hours.
Choose your layover on whatever basis you like, but lost bags shouldn't be an issue.
I cannot imagine 10% of luggage ever misconnected in AMS. This just seems sooooo much higher than anywhere else. Moreover, it would imply that KLM as the major user of the airport would have a rate of mishandle luggage at around 10%, which would have put them in an untenable business situation.
More importantly, what matters is the mishandled rate now, not way back when: the rate for 2017 was 5.57 per thousands, and Delta now uses technology where they claim to handle 99.9% of all bags perfectly (as reported by the BBC here). Given that AMS is a major Delta hub, and KLM is so intertwined with Delta, it is unlikely that the DL performance is much worse than announced when connecting to a KLM flight.
As an aside: I avoid CDG as much as I can. I have always found AMS to be much more passenger friendly: clean, with a logical layout, and spacious wait areas, all things which CDG is NOT.
Last year I was part of the software team of sections of the baggage handling at Schiphol. From the data I saw there they never reached the 10% you claim. The year I was working the number of lost bags was 0.75%. Which is lower than the European average of 0.8%. Though that might be because of the number of significant digits.
From my own limited experience (fly once or twice a year, always from Amsterdam), luggage handling was very bad in the '90 but is good now. On returning home i hardly ever have to wait more then 15 mins for the luggage to arrive on the belt. Only once had two bags misplaced, they were sent after us on the next plane, this was about 15yrs ago.
It used to be in the '90 we had to wait for 45 mins normally and very often they would forget to unload or would only unload half the suitcases. Than after complaints and some more waiting the rest would come.
As others have stated the loss rate you quote is probably a misquote, and these days probably irrelevant. Faster connections <1h increase the risk of luggage missing the connection, but they'll send it to you on the next flight. So if you're worried about late bags, pick the airport with the longer layover. Or better yet, plan your flight so the connection has 2h-3h as a layover.
On a personal note, i agree with the comments that AMS nicer than CDG, but that is personal taste. Also AMS is more in English then CDG, which is french after all.
I think I remember from years back when there was a strike or a system failure there was a huge backlog of luggage in Schiphol, it may even have happened a few times when they were installing the current luggage system.
But that was years ago and I have not heard about system failures for a long time.
If there was a 10% luggage delivery failure it was to deliver in a timely manner, all delayed luggage got send on bar for a small percentage which had lost tags.
It was also always short in duration, like a 24 hour strike.
So while there might have been a time when the 10% luggage lost was mentioned in the news, it was never a long term number.
Strikes can happen but are much less likely in the Netherlands than in France, so based on that alone I would avoid Paris.
I have written this answer from memory, living near enough the airport that news like that makes the small, free, local newspapers and the local gossip.
The 10% figure was/is total nonsense
It seems like on the order of 1 to 10 in 1000 bags get delayed or put on the wrong flight. They're not lost, you just get them late.
(Example, I once flew from Paris -> HK -> Sydney, and by mistake they sent the bags to HK. They dropped them off to me in Syd. the next day.)
Regarding profoundly lost bags (perhaps stolen, or just utterly lost - you never, ever get them back). This is extremely rare.
Regarding Paris versus Amsterdam on the issue of delayed baggage. Absolutely no difference whatsoever.
Note that if the baggage gets delayed, that will very likely be due to the airport you start in, New York or whatever. For example someone simply pressing the wrong button or entering the wrong code. The "middle airport" would not affect this much.
The general answer to your question is simply that there is utterly no difference in choice between Amsterdam and Paris in terms of the luggage issue.
Purely FYI: Never, ever, EVER fly to or through CDG!
CDG is a hellhole, and Amsterdam is one of the two top of the world's very-large airports. So choose Amsterdam!
Note that even if you're going TO PARIS for a holiday, for goodness sake, fly to somewhere awesome like Lyon, Zurich, etc. and take a train or drive in to Paris! CDG non. (The only thing worse than CDG itself, is, the commute from CDG to Paris!)