The 9006 bulb doesn't leave as much room as the H4 to fit in a lot of Xenon gas, so they will never be as white as advertised. So when companies/people declare how great a bulb is, be wary of what sort of bulb they are using.
As for cheap aftermarket bulbs, I highly recommend Eaglite. Sure, they run at 80-watt and may burn out your wires, but they are, by far, the whitest (with a tint of blue/purple) light output I've ever seen. All other brands for the 9006 series fail by comparison. I've found, after buying a whole mess of various bulb brands, the bluer the glass tint, the whiter the light output will be. Eaglite have the darkest blue out of all of them, yet still has a good output for illumination. Check out
http://www.midnightmoose.com to order for cheap.
As for Piaa, I haven't tried the SuperPlasma series yet, but I would probably recommend those over the regular SuperWhites. I bought the SuperWhite and they weren't anything special to talk about. I'm a bit hesitant to buy the SuperPlasma's, but looking at the pictures they seem to have that mirror/clear tint, so I guess they rely more on the gases inside rather than the glass to change the color. Should be a better.