Best internal temperature for chicken?
The USDA recommendation for a safe internal temperature is 165 degrees for chicken.  The breast, being leaner, shouldn't be cooked to any higher than that or it will dry out and be tough.

The thigh can be cooked to a slightly higher temperature (165-175).  That is the Kitchen Network's preference for taste and texture (link here).  Getting the thigh to a slightly higher temperature (and keeping it there for longer) helps the collagen break down, which will make it more tender and taste more moist.