The Kenwood L07D comes with a 5-lb stainless steel mat, a la the one Albert describes. I am a big fan of my L07D with this mat. I also like the SAEC SS300; like the M-S mats, it's no longer made but usually can be found on Audiogon or eBay for sale. Boston Audio Mat1 and Mat2 would be in my top 3. So, interestingly to me, Albert and I are in nearly complete agreement. (If I ever audition an M-S mat, I am sure I would like that too.)
As far as the stock rubber mats typically supplied even with the best vintage turntables, I feel about them the way Joan Crawford felt about wire clothes hangers (if you remember the scene from "Mommy Dearest").
But I thought the OP wanted to talk about platters, not platter mats. To that I would say that if you use one of the above mats, the composition of the platter per se becomes much less relevant.
As far as the stock rubber mats typically supplied even with the best vintage turntables, I feel about them the way Joan Crawford felt about wire clothes hangers (if you remember the scene from "Mommy Dearest").
But I thought the OP wanted to talk about platters, not platter mats. To that I would say that if you use one of the above mats, the composition of the platter per se becomes much less relevant.