The best one is the cheapest, most reliable and most efficient one
Who makes that is completely debatable. Outside of on the Z, I know many people have used this oil cooler without a single issue or failure:
Oil Cooler Kits - Oil Cooler Kit with Thermostat
Don't know of anyone with a Z that has them, but outside of making a simple bracket, I don't see why this wouldn't work while coming in hundreds cheaper than others ::shrug::