Cat 5 - 6 -7 or 8

Cat8 can produce ground loops between connected components through the unshielded metal plugs. Otherwise it all depends on connectors, shielding and quality of copper used. I have good experience with cat6 Meicord Opal. Also using an EMO filter for galvanic isolation helps

@eric_squires,

your answer applies in low density, rural areas. Anywhere else, and in particular near radio and telephone masts I'd stick to shielded.