Platform for amp

IMHO neither. Both will transmit vibrations in both directions - I would opt for some isolation materiels which would reduce or eliminate the transmission of vibrations, especially if you referring to tube amps.

Definitely not granite, it stores energy and it rings. I plan to use maple butcher block on Walker Audio Valid Points with my tube amps (100lb monoblocks) based on what I've heard in other people's systems.

Alternatively, many people report great success with platforms that will not store energy such as Neuance shelves from Greater Ranges or Sistrum platforms from Star Sound Technologies. There are others.
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As much as I was enjoying my system it got even better when I placed my 845 tube amp on maple with brass cones. The improvements were even more substantial when I did the same with my tube pre. Good luck.

Cheers

I like the Sound Anchor amps stands. They look and sound great and can be tweaked using Vibrapods between the amp and top of the stand and replacing the spikes with Audiopoints or your favorite cones.

Disclaimer: I'm not affliated with or sell any audio/video equipment.

Or you could just cut yourself an appropriate sized piece of 3/4 inch MDF which you can get down at home depot. Cover that with the sound damping vinyl sheets you can order from Parts Express and for a whopping investment of about $40 you can achieve what otherwise might cost you hundreds, even thousands for the voodoo audiophile solutions.

Nick