Unscientific Diffuser/Bounce test:
LumiQuest Pocket Bouncer and Sto-fen Omni-Bounce Direct - Left: no diffusion. Right: With Omni-Bounce45 degree- Left: no diffusion. Right: With Omni-Bounce90 degree- Left: no diffusion. Right: With Omni-bounceLumiQuest - Pocket BouncerCamera setup: Nikon D80, Program mode, White Balance, daylight. Flash - SB600, I didn't flip the built-in diffusion of SB600 over the lens.
Looking at these pictures, I am pleasantly surprised that no diffuser, 90 degree (bounce off of ceiling) is my top pick, but I find direct and 90 degree with Omni-bounce to be very close, and pleasant.
For convenience, it's more likely for me to use the Omni-bounce. Remember, this require a little experiment for different conditions.
Another product, that I do not have, but have seen the result, is the Gary Fong's Lightsphere. I don't know why, but the way Lightsphere spread out the light makes it really nice on skin tone.