By far the Wing Mfg P-38. It was the short kit and part of the problem was that it was the first time I had cut parts from plans. When they didn't fit, I had a professional builder I know re-cut them and they still didn't fit like the (rather lacking) directions said. It took almost a year to finish it, including glassing and painting, with lots and lots of cussing, but it was impressive in the air powered by 2 YS-53 four strokes. Now that I have that experience, I feel I could tackle almost anything, even a Marutaka which, by the way is my next project. Another P-38, of course.