Both great ships. The 20 is about 50% stronger when it comes to surviving a full blown ground-loop. The gear in the 4 wont take much side loads and the cockpit has been known to open up like a can of sardines. I have repaired two of them where the canopy glass and frame broke, that allowed the cockpit sides to spread outward, leaving the pilot sitting in a pile of fiberglass rubble.
Also, any kind of clam-shell trailer is much better than any tube type trailer. You will have to bend over anytime you remove or replace the wings...............Oh, my aching back!
JJ