Both have there strengths.
Photoshop: Layers, Adjustment layers, Layer masks, Levels, Curves, Shadow/Highlight adjustment, Image Size command, Camera Raw, Image Processor script in CS2, Browse to Bridge, Healing Brush and Clone Stamp
Flash: Frame-based timeline, Shape primitives, ActionScript 3.0 development, Sophisticated video tools and so on
Basically I will say if you are looking for action scripting then have to go with flash whereas for photo/ static stuff photoshop.