It would depend a bit...
If you will be installing a supplemental brake system then the 10K rated tow bars are probably overkill. On the other hand, if you choose to not use supplemental brakes, then the 10K tow bar would be a much better choice in my opinion. All that momentum hitting the tow bar every time you hit the brakes will wear out an adjustable arm towbar over time.
If you are considering not having supplemental brakes, I hope you will read this article first...
The Physics of Towed Vehicles