Have done both lines over the past 14 years but none since 2019 due to Covid.
Close to Diamond on Seabourn and about the equivalent level on Silversea.
In our past experience, the overall difference between the two is negligible.
Yes, there are slight differences of course. The coffee is better on Seabourn and the pizza is better on Silversea, among many other very minor things. It’s just little stuff, they are both excellent.
I did a post about the comparison between them maybe 9 years ago. Maybe you can find it!
For our now finally resumed cruising schedule, we have based our decisions on which line purely on itinerary.
CJ