Best type of metal for turntable platform?

If you need vibration reduction you want an isolated wood not metal under a turntable but if you want to you should use brass as a metal nothing else.but a thick wood shelf about 2 to 4 inches thick of laminated wood like a butcher block will work best.

I would try a sandwich of Acrylic, Aluminum, and MDF to vary the density of  the materials.  A liberal application of silicone caulking between them.

Build a sandbox very very effective and cheaper!!!!!
Rob

I have a Townshend seismic platform (it has pods attached under it) under my turntable. When installed, it improved the sound so much I was incredulous. Unfortunately, the very low waves from the pods combined with my suspended floor and extremely light turntable created footfalls that didn't exist before (to anywhere near that degree). 

It was either live with the improvement and tread lightly or go back to square 1. I was going to live with both because of the sublime sound. But, guess what - I put in a wall shelf ($179 from Project) and put the Townshend platform on top of that. All problems solved and the sound improvement had to be heard to be believed. I was very skeptical.

I like the platform better than the individual pods because there is no fiddling around with placement. You can adjust the springiness in each spring to level the platform for items that have lumpy weight distribution.

@millercarbon takes a lot of abuse from some posters, but I have to thank him for turning me on to Townshend. I had the privilege of talking to Max himself a couple times - extremely nice down to earth guy, very honest - kind of like a mad scientist who does his own research and has solutions that work. When he starts talking about continuous earthquakes, he is on to something.

Wall mount, better shelving/ rack- 
better table, feet - so many options , solutions 
Many May cost less than suggestions so far-
Have had problems w “footfall vibrations “
Better turntable, racks, footers, cartridges, have helped for different situations.
From my perspective, no one size fits all