With a single axle trailer I would say it makes no difference. On dual axle trailers with a equalization bar between the axles... no difference within reason on amount out of level. On a trailer with Torque Flex axles... no equalization between the axles towing low in the front will will decrease the amount of tongue weight resulting in the trailer wanting to wag the dog.
I have a 31' Airstream that I would like to tow with the front low so the back drags less often BUT with the Torque Flex axles this makes it want to sway. I'll probably lower the rear axle 1/2" to make it possible to tow it front low.