Given 2 speakers at the same price point, the floorstander will involve more materials, so could possibly lose out on driver quality.
Let's assume that the drivers, for the sake of argument are the same size and quality. The standmount(SM) has smaller cabinet panels, which tends to be less resonant compared to the larger panels of the floorstander (FS), which needs more bracing to achieve the same ridgidity, adding to the overall cost. Because of this, the FS cabinet joins in with the proceedings, adding a sort of 'bloom' or warmth to the sound, which isn't accurate, but preferable for some. The SM in comparison sounds tighter, leaner, and usually more accurate. The same can be said of the cabinet volume of the two types of speaker - SM speakers have a smaller cabinet volume so sound a little leaner, whereas FS speakers have larger cabinet volumes, so can sound bigger, fuller, and deeper.
For me, depending on the price point, because of the above differences, a SM speaker can produce a more 3D image, because it's leaner, more solid, and producing a technically more accurate sound. Once enough money can be put into a FS speaker, these differences lessen, but are still noticable.
Which the individual prefers is up to them - but the room will also affect how these types of speakers perform in a room (which are all different). Another aspect that affects speaker performance is whether or not the cabinet is sealed, rear ported, front ported, transmission line etc etc.