And your preferences can vary betwee instruments... For instance, my Explorer sounds best with the tone knob (Single knob) on MAX all the time since its got the 496r/500t pickups in them and they already sacrifice brightness for strength and it already has a dark sound to begin with from the mahogany.

However on my Stratocopy (I have the switch wires reversed so the bridge pickup has a tone control, but not the neck), I roll off the tone to about 6 or 7 to keep that overbearing jangle under control (Keep in mind I have a hot-blades in the bridge). I also do this with the Seven-string but thats because the pickups sound like @ss and rolling back on the tone a little helps the sound some... but this is my experience, but when I roll off the tone, I tend to lose a little grind sound at the same time. It probably has as much to do with your amp's settings (I'm pulling this out of my hat) but I usually keep my tone as high as possible (I would have to guess that most of the amp's frequency response is in the mid-treble range, and cutting that frequency with the tone control reduces your overall response at the amp)

I pretty much use these settings for everything I play, though I have been known to mess with the Stratocopy's tone-knob for a little bit of a wah-wah sound.