Which BBQ grill conversion is easier. Natural gas (NG) to propane or propane to NG?

I'm looking to buy a new grill and I'm not sure which to buy. I'm leaning towards natural gas because its cheaper and more convenient, but if I decide I want to be able to take my grill on the road (camping, tailgating, etc) I want to have options. Also, once it's converted is it easy to switch back and forth?