Any ground screw or bolt would be fine electrically, but you want to make sure that it's not a screw or bolt that could cause problems when loosening, you have clearance from anything that might grab it like a branch,root, or whatever. Away from anything that gets hot like the exhaust. Just some common sense when running wires, you know? you don't want the wires to be damaged or them to damage anything either.
Make sure you have an inline fuse close to your power source.