The suspension on a flatbed truck will likely be much stiffer since it is likely designed to carry a much heavier load than a glider in a trailer.

I would choose the bidder who will tow it behind a truck due to this. The suspension on a good glider trailer is designed to carry the weight of your glider without undue stress to your glider.

I would also like the person towing the trailer to make at least a couple stops along the way and open the trailer to make sure all is well. Don't ask me
how I know this!