Speaker enclosures (or frames, in the case of stats, maggies, etc) MUST NOT MOVE, PERIOD, THE END!!
If an enclosure can move, usually noticable as a slight rocking fore and aft or side to side, near the top of the enclosure, then not all the energy of the drivers will be transferred to the air. In addition, other nasties, such as doppler effects, are added to the acoustical output of the drivers.
That said, it really all begins with the floor. It must be as steady and solid as the earth itself. A concrete slab poured over a gravel bed (typical in residential construction) is best. A three point footing assures no wobbling (that's why cameras and telescopes are mounted on TRIpods).
How the speaker enclosure is attached to the floor is unimportant as long as it CAN'T MOVE. If the speaker is HEAVY enough, hardened metal points (spike or cone) securely anchored to the bottom of the enclosure will provide sufficient "bite" to "mass-couple" (a fancy word for "attach") the enclosure to earth.
Conditions are often less than the above "ideal." The speaker itself may not lend itself to a solid connection to the floor (think monitors on stands) and/or may not be heavy enough to provide stability simply from force of gravity. A wooden floor structure (wood joists with a plywood subfloor on top) will always allow speaker movement even with a three spike arrangement, because the floor surface itself flexes. Even the bottom of some less-well-made enclosures themselves flex. (Placing a sandbag on top of a monitor/stand helps but isn't pretty.)
In these cases, there is really only one other mechanically sound solution. It's called triangulation. It involves using a strut of some kind (I've used thin wall 1" dia aluminum tube). Place the speaker on just two spikes left and right side and positioned front to back so the speaker naturally wants to tip toward the rear. Attach a strut from the top rear of the speaker to the back wall. There are many elegant ways to do the hardware at the speaker and at the wall, I won't go into that. A variation, if the speaker is more than 4 feet from the back wall, is to tie the strut down to the floor behind the speaker.
There are some other tricks when dealing with a joisted floor to provide a more rigid platform for the speaker. Floor joists are usually 12 or 16 inches on centers. First, find out which way they are running. tapping the floor can usually tell you, but most probably, they are running across the short dimension of the room. DO NOT place the speaker centered over ONE joist (ie straddling it fore and aft) This allows maximum rock when the floor flexes. Instead, place it BETWEEN two joists. This positions your front spikes near (maybe even over) one joist, and your rear spike near (maybe even over) the other. Choosing the placement carefully this way can make an enormous difference in improving transient response.