What is the ideal?

Question

towing hitch weight for fuel economy. when pulling a caravan?

Answer 1

The nose weight is irrelevant to fuel economy: You have the same weight & drag regardless of how it's distributed throughout the towcar & caravan.

Answer 2

As JG says - the nose weight won't affect the fuel consumption  But it will have an effect on the handling and braking of your rig. You should be able to find the correct nose weight for your car in the owners hand book.