Plate mounted switches all the way!
PCB mounted switches do feel a little "softer" depending on the board design and support from the case, but plate mounted switches feel more "mechanical" and precise to me. Keycaps can have a very big effect on the switch feel, though, so a perceived difference between two boards may not be primarily due to the plate / no plate, but rather a difference in keycap mass / quality.
Also, almost every PCB mount board will feel different to each other. For instance, my KBT Pure felt almost like a plate mounted board compared to the mushy unsupported G80-3000 boards of mine. Same switches, same keycaps, both PCB mount, but very different feeling. I have since installed a plate in the Pure and it feels even better than it did before. I don't like the mushy bendy soft feeling of a poorly supported PCB mount board. Well supported PCB feels better, but going full plate mount with good keycaps feels best, IMHO.