The best setup I've found is what I lucked into at work. It's a Benq monitor (32", 4k) that does the KVM itself. There's a couple of Displayport inputs, each if which has a couple of USBs with it, as well as a USB C which is both peripheral and display input (and decent power output). Then there's a little pick on the desk for switching.

The nice thing is that it continually presents a monitor to all the inputs even when they're not being displayed. Means you don't get the flickering as Windows sorts itself out and so a much faster and more seamless switch.