This subject has been beat to death in the formus. The general concensus is that square trailing edges are less likely to cause flutter. This opinion can be found in numerous written articles. However, due to the small size of our models, I gather that the effect is very small and that you can pretty much do as you wish with trailing edges. For the racers, sharp trailing edges do reduce drag. Much more important in reducing flutter are strong control surfaces, rigid control mechanisms from the servo and keeping the center of gravity of the control surface as close as possible to the hinge line. I always taper the control surface from the hinge line to the trailing edge and have only had one flutter problem on 25 models, including many lightweight fun fly types. The flutter problem was on a stick where the ailerons got wider towards the wing tip and extended all the way to the wing tips. It was easy to fix.