Best vibration isolation for speakers on carpet?

I had a pair of Revel F32 speakers using the spike feet combo that comes with the speakers. I bought 3rd party outriggers to replace the spike feet. Positive major difference for speaker stability. Bass clarity and detail improved as well though it was a minor improvement compared to speaker stability. 

Good thing you didn’t go with the Gaias because they are a nightmare with carpet, especially thick carpet. 
 

One thing I’ve learned over the years is that when leveling spiked speakers, you often have to adjust the spikes by only small fractions of a revolution (like 1/6th) in order to get all spikes firmly contacting the substrate. So you feel the speaker rocking at the top panel and think maybe one whole counter-clockwise turn of the short spike will do the trick when in reality it only takes 1/2 turn or less. 
 

Wooden subfloors make this even trickier because you have to account for the spikes penetrating the wood and over time they settle. In those situations you want spikes with a wide cone angle similar to the Dayton Audio ISO-4C. 

For those with speakers which incorporate outrigger bases---and for those who added after-market outriggers to their speakers, individual Townshend Audio Seismic Pods may be substituted for the spikes routinely supplied with outrigger bases. Good outriggers fitted with Pods are just as effective---and cheaper---than the Podiums (as well as the Seismic Bars).

Actually a good cabinet shouldn't be conducting sound in the first place, but anyway....Spikes are as effecient at sound conduction as other feet.  They are simply a contact allowing vibrations to pass.  Sonic conduction does not care that they look like a one-way arrow, it just cares if there is a connection - or not.  If you want no connection, then get no connection.  Place them on an air isolator.  Try out some tennis balls for starters.  See if you can tell the difference. 

There is no “best” - that can only be judged by the ear of the beholder - you.

in general, there are two camps, coupled (i.e., using spikes) or decoupled (i.e., usually on an elastic support such as a spring or elastomer, but sometimes on a hard support such as DH Cones or a ball bearing solution.

Back in the day, after footers became a thing, conventional wisdom was to couple with spikes with the possible exception of speakers on a suspended floor over wood joists, where a growing minority started to believe decoupling sounded better.  Currently, people seem to be split as to which option they like best.  

Within each camp, the options range from very basic or DIY-type solutions to very expensive items that are often marketed as “the one best solution.”  

Spike options range from the simple hardened steel, threaded Ramset spikes used by Sound Anchor to large brass footers from the likes of edenSound or Mapleshade.  Townshend has the most popular spring solution, although simple springs can work too.  Herbie’s products may be the most popular elastomers, but there are a variety of silicone or sorbothane based elastomeric footer products available.  You will get many specific recommendations from the folks on this site.