More flexibility and (usually) better bass with (at least two high quality) subs.
Stand mount main speakers can image better but the output capability must be sufficient for the size of the room you are trying to fill. Puny stand mounts with subs doesn’t work for me. I would look for main speakers that legitimately cover down to 50 Hz, or a bit lower, so the subs are only covering the bass. It is better if the stand mounts are designed to operate optimally within their given frequency range and do not attempt to cover the lowest octave using their small’ish drivers, which can muck up the bass and the midrange.
As @ghdprentice pointed out, it is also very important to roll the subs in carefully and not run them too high or too loud, as a little less is often just right.