both are on legs and I have a 12x14 which is a stand mounted floor tom, yes there is a huge tonal difference between a floor tom with legs and one without and there is a significant lower end tone that you cannot get from a 12x14 verses a 14x14 floor tom.
You can come close with dropping the tension of the bottom head on a 12x14 but not quite enough, if you have the oportunity I suggest sitting them side to side and trying for yourself.