Yep, this is definitely Germancarforum
I'll gladly buck this trend.
When I sat in the S90, the feeling I got was relaxed. The seats were supremely comfortable. The look was modern but will stand the test of time. The walnut inlay in the Inscription trim looked and felt like genuine wood and not the plasticky wood trim seen elsewhere. Sorry, the wood trim in both glossy and matte finish in both MB and BMW today feel chintzy, especially when compared to the wood trim in the 1990's which felt more substantial, especially with MB's of that era. Everything felt nice to the touch. The digital gauge cluster was good, but looked half a generation behind its competitors. The big blotch against the S90 is the touchscreen interface. It's better than many other competitors' touchscreen, but nonethless, you still would have to take your eyes of the road more than you'd like to do anything. BMW still leads the pack with the iDrive 6.0 and the 7.0 iteration looks the further that distance. My hat goes off the Robin Page's interior design team (also Thomas Ingelsath's exterior team).
Which leads to the 2nd place: BMW. The interior looks like it has been constantly evolved upon, but damnit, it just works. I was debating between the BMW and MB for the second spot. Sure the MB has a bit more drama, but day in, day out, I'd want to deal with BMW's UX and interior ergonomics than MB's. It just makes sense.
3rd: MB
4th: Quality interior, crap UX.
5th to whatever: I am ambivalent. I will say this: though they've come up short, the interiors of the American entries have made greater strides in the modern luxury interior realm. They still need to go farther.