For what it's worth -
My layout (8x12 with FasTrack) version 2.0 was 1/2 inch rough pine (cheap) plywood with 1/2 inch pink foam board glued on top. The foam had many advantages in terms of easy painting but anything that I wanted to fasten to the top (like track) was difficult because you can't bite into the foam and you need to drill down into the plywood itself. The foam can often chip and (because of the size and configuration of my layout), I needed to climb on the table frequently (frame is 2x4s) to work on building placement and scenery. This left many dents in the foam. I guess it was self-made terrain features and I lived with it. I didn't find that the foam dampened the FasTrack sound much and it seems that many people agree there is not much you can do about that anyway (wish I had started my modeling adventure with Atlas track but too late now). For my layout version 2.1, I am now trying nominal 3/4 inch sanded birch plywood painted with no other surface material. It is plenty smooth, no need to worry about dents and chips, and much easier to affix the track with conventional track screws. Have not finished yet so I am holding my breath to see if the noise is really any worse than with foam. I read many opinions on the best layout surface with seemingly little consensus, so I just decided to try the experiment. Half of the layout will have foam top (version 2) and half will be straight plywood (version 2.1).
