The standard size, 24" square, is more aerobatic. It spins tighter and faster and is more radical in general. The 28" square is better at slow flight. It is more stable at slow speeds and Harriers and hovering are super easy. They weigh about the same and the bigger one has a much lighter wing loading. I have one with a Saito 30 four cycle on it and it is such a pleasure to fly at slow speeds and in the wind it is a ball to fly. You can get it flying sideways slowly about 5 foot off the ground right in front of you and it does all this like it is in slow motion.
Here is a tip for all PBF flyers. IF you cut the engine to idle you can let the nose down and it won't do the death dive. It is easier on a windy day to bring the plane in to land because if you keep the nose up at low throttle in the wind it will hardly sink and it takes forever to bring the plane in to land.