What your choice speakers with spikes or speakers with a vibration isolation device?

Max Townshend covers the issue of Newtonian forces in one of his YouTube videos. Prepare to have your assumptions challenged.

I just use the spikes that came with the speaker.

Speaker cones should move but NOT speaker enclosures.

In my experience, the choice between coupling/spike and decoupling/isolation will depend on the type of floor the speakers are sitting on. If the floor is inherently isolated such as concrete slab, tile on concrete, etc., the spikes work well. Similarly, spikes seem to work well on carpeted floors as well. On suspending wood floors, decoupling is a much better choice minimizing the potential vibrations/resonances from the floor coupling with the speakers muddying up the response, particularly at the lower frequencies.

Vibration coupling, isolation or absorption (turn motion into heat) are different approaches to tuning, which means that, to the extent they change the sound, such changes can be positive or negative.  That means you have to experiment to see which result you prefer. 

As kalali describes above, coupling devices like spikes often are not the preferred approach on a suspended wooden floor because the transfer of energy to the floor turns the floor into a sounding board.  I have carpet over a suspended wood floor and I use a Symposium Svelte Shelf under my speaker (the entire bottom of the speaker sits in contact with the shelf, the inner foam core of the shelf turns the vibrations into heat as the vibrating molecules in the core rub against each other).  The Townsend devices work on the same principle.  This tightens up the sound and makes the bass less boomy; whether this is good or bad is a matter of system tuning and taste.