Amsterdam Schiphol Airport (EHAM) would definitely be the go-to spot if you’re in Europe…
It has loads of spotting locations, a few official, a few unofficial.
for an interactive map, visit Amsterdam Schiphol Spotting - Google My Maps
The best spot is, by far, Runway 18R/36L (Polderbaan)
This spotting area has a car park and a chipper. Additionally, it has a path that goes parallel down the entire length of the runway, so you can choose the best location for your photos. This runway is used almost all of the time.
This one is just before the touchdown marks, after a good walk down the runway.
This one is at the main spotting area (at the car park)
And this one is just after the touchdown marks
You also have an official spotting area at the McDonald’s to watch plane landing on 27/taking off from 09 or takeoffs on 18L. Unfortunately, I haven’t been able to spot there, as every time I go, these runways do not get used.
After the Polderbaan (18R/36L), the Kaagbaan (06/24) gets used the most. There are no official spotting areas for this, but there are more than enough unofficial places.