ALWAYS choose the hard surface.
Skids: Get sideways in the grass you and might tip over.
Wheels: Same idea.
Wheels on pavement: Nose dragger it will kick straight. Tail dragger you can pedal it straight.
Important thing is, tipping over is much less likely to happen on a hard surface.
And don't worry about grinding the skids (or wheels) - we can always buy new ones
