It really depends on how you get onto the rail.
Some people slide rails with their skis perpendicular to the rail, with their shoulders facing somewhat forward still, this would make it easier to come off regular.
Some people slide facing fully sideways, or even backwards, and would have more momentum backwards to come off switch.
At least that's how I set myself up on a rail to come off the way I want.
Same with 270s off, if you turn your shoulders slightly in the direction you are going to spin, it makes it easier to spin off.
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It's the batontwirlertwistshakebakecakeholehumperdinkkink rail.