Tow dolly advantages: significantly less tongue weight (even though within the RV's capabilities, this can be still be relevant in many cases), less stuff to find space for at a campsite, nearly always no need to register the dolly, easier to manhandle around for storage, possibly lower initial cost.
Trailer advantages: you can haul other stuff if the need comes up, no wear and tear on the rear tires/bearings/etc. of the towed vehicle, fewer limitations on what other vehicles you could haul, backing up is possible (but not especially easy with a short trailer connected to a tow vehicle with a long rear overhang).
Personally, I suspect I would end up opting for the dolly, but I'd certainly give both options a good bit of thought first.
