Worst kit was the Hal DeBolt Patternmaster. The wood was ok but the construction methods were sadistic! Before starting the kit you had to construct several assembly jigs and fixtures. The stab was a little wing itself. The instructions had you glue balsa cradles onto the fixture, then mold the sheeting the cradles. The ribs were then glued onto the sheeting, etc. The wing was built full span upside down using more cradles on a building board you had to make with 4 degrees of dihedral. Insane!

I also have bad memories of the PT40 by Great Planes. Construction was fine but it needed constant fiddling: big flat bottom wing, tons of downthrust, etc. I hated flying it so much I flew it into a barbed wire fence.

My best experience to date was the Proctor Nieuport 11. There were a million parts and it for together like a Swiss watch. Very therapeutic.