It kinda depends on how you plan on initiating the pretzel. If you wanna do the scissor thing you're gonna want to do it on the rail because it's hard to scissor on a wide surface.For pretzels though you can also just dig both your edges down into the box/rail. If you do it this way it would be easier on a box because this motion can be done on either, but it'd be easier to balance while doing it on a box.