generally i would say its easier to learn stuff on boxes, but if you can 270 onto rail good i would say that its easier to scissor on rails to spin off.
if you can do 270's onto a rail i wud do it on them but have u tryed gas pedaling? it makes it so much easier to get the 270 off
its hard to explain but gas pedaling is after u 270 or w.e your doing on u take ur front foot an u tilt it so its on its edge and this stops your rotation and makes it easier to spin off
otherwise known as a scissor