APC 13x4w or 14x4w. (w=wide blade) Just watch your clearence. Maybe even the 12.25x3.75, just watch your rpms.

Low pitch+large diameter=thrust. For 3D you want thrust. You dont want speed at all, lots of the 3D airplanes can't handle the speed, for one... but you want pulling power for 3D so you can have authority while hovering and the power to pull through some of the more demanding manuvers.

Steve