It's pretty subjective but I would say for TATL:

KL has friendly service always happy
AF has better wine and food especially wine
DL has better nonstop routes otherwise average
VS has more "fun" cabins and probably the best J lounges in my opinion (note priority pass access is not the same experience)


You'll see what you get on the seat for each aircraft to make the trade offs there, along with the cabin pressure benefits of the A350 and B787. The service routines are pretty much the same: meal and drinks after take off followed by a very rare cabin walkthrough then second meal service before landing. AF and VS have the advantage of open snacks and alcohol area so you don't need to find a FA for a drink. KL just has snacks and water, and DL sometimes the same.


Personally I like to book a 3 hour layover in Europe inbound and shower in the lounge before heading to my destination arriving nearer to check in time. In that case AF is a bit better than KL both because of the lounges and the on board offering for a domestic EU flight. Domestic KL food is not as good and the wine is poor but no big deal for a shorter flight. If you do go KL note the intra EU lounge 25 in AMS has terrible showers.

On the return I usually take the last westbound flight which is usually KL or AF because DL wants their flights to feed connections and keeps them a bit earlier.

Still I would pick DL if they had a nonstop for a fair price and just pay for arrival showers or day hotels.