Vertical works better with my current setup and I can agree that the stand makes the console wobbly when it's horizontial. I had to move the tv slightly to the side because the console wouldn't find in a shelf where I wanted to put it.
They said the same thing about the PS4 pro as well.
I actually think horizontal looks better. The console design looks horrible though. The PS4 slim and pro were such good looking consoles (esp in horizontal).
I think in general I find horizontal better looking, except for Series X.
Either vertically or horizontally I had some pretty noticeable vibration as well. I stopped that by removing the top cover and placing a bit of foam in the area that was vibrating and them shutting the lid. You can't see the foam sticking out and my console is vibration free!