It's a matter of preference imo, both are used. In fact in 3D modelling tools, like 3D studio max, when creating a box for example, you are asked to enter width/length/height. Because you use these words daily when defining the size of objects, it should be familiar terms.
I don't think it's the most urgent problem in openxcom at the moment, better we spend our valuable time (our _Tsize?) in fixing horrible things like aliens seeing and shooting through the roof of the Skyranger... I was kinda shocked during the last stream, I've never seen that happen before.