Which cone's or platforms have helped?

Sugarbrie what you said...
I've been aware of this too, & found that the Vibrapods need to be loaded basically at the midpoint of their weight range. Just requires some simple math to calculate where you're at. It's like the springs on a vehicle; too little weight-loading & you're bumping all over the place, too much loading & you're always bottoming out. At midpoint, you have some "spring" in both directions.
YMMV

I have used several highly regarded isolation devices. Vibraplane, Black Diamond Racing, Walker Cones, Aurios and Townshend Seismic Sinks to name a
few. In my system the Tri-Orb Lite reference grade isolation devices
provided hands the ultimate in vibration control.

I have gone for isolation, not coupling, and have been most pleased with Audioprism's Iso-Bearing polymer ball in delrin cup footers. Stable, effective, and fairly reasonably priced. Symposium shelf is under the TT, but MDF or wood shelves otherwise, neither of which seem as though they would be optimal when you knock on them. In general, I have found the differences to be marginal at best. I readily admit to not having much interest or patience (or faith) for this kind of thing, though...

When and if you use a loading device it should be a solid metal. Not sand or lead. The idea is not to absorb vibrations, but transfer them to the ground. There are many vibrations that are good and you don't want to lose them. Robert over at Star Sound Technologies is doing some amazing things with this concept. His precision made brass cones are doing the job, and his speaker stands and component stands are drop dead amazing. Both, utilizing the resonance transference concept. I truly believe that his stands are the cutting edge, and it's just a matter of time before they become a ubiquitous HI END name. All your components sit on a stand. You want the bad resonances to move away from your equipment and go to the floor. .

Last night I put the Mapleshade Heavy footers under my transport that is sitting on a seismic sink, my 16 yo audiophile dughter and I couldn't believe the difference this made. The bass was much tighter and everything was more in focus, the pace of the music even sounded better.
For the price I think they do a great job.