Where are the best bathrooms in the parks?

My vote: Epcot: Japan. Way in the back, above the pond, next to the quasi-fast food restaurant. Nicely themed decor. Small but cool, quiet, clean. Kind of a secret really.
The ones inside Mexico, way in the back (inside the restaurant area) are busy but otherwise aren't bad either, since while you're waiting for whoever, you can shop under the starlit skies of Mexico, and listen to mariachi. Aye-yi-yi!
For worst, I'd have to say several of the ones in MK and DLR near the castle, since they have little or no theming, very busy, are often filthy (by Disney standards at least), and with two entrances/exits easy to get lost in/out of (or to lose kids at!).