Towing glider trailers can be readily split into two areas. retrieves where
you might have to drive down farm tracks and accross fields and road
towing.
For retrieves nothing beats a 4x4 with plenty of ground clearance. The
limiting factor is usually the trailer.
For road towing a car is usually better as they are much more economical to
run.
Size and weight are important but not at the expense of decent suspension.
For example I had a very interesting 30 seconds with a Nissan Navara towing
a K21 in a cobra tailer. The same trailer behind my VW Passatt was much
more stable. I put this down to the Navara having leaf springs on the rear
with poor lateral location of the axel. The Passatt with modern suspension
was much more precise.
So far this year I have driven 3500 miles across europe towing a variety of
trailers in the passat averaging 43mpg (36 us mpg) The navara was in the
mid 20s.