My favorites have fluctuated a lot throughout my life, to be honest. It's hard to pinpoint exactly where a given character falls, really.
As a kid, it was Mars, Jupiter, Venus, Mercury, Moon, Chibimoon (unless you add the Outer Senshi, then it was more like Saturn, Mars, Jupiter, Venus, Pluto, Uranus, Neptune, Mercury, Moon, Chibimoon).
If we're talking current favorites, accounting for everyone, it's probably Star Fighter, Star Healer, Jupiter, Mars, Uranus, Pluto, Saturn, Venus, Neptune, Mercury, Star Maker, Moon, Chibimoon.
With just the Inner Senshi, it'd be Jupiter, Mars, Venus, Mercury, Moon, Chibimoon.
Really, I like just about everyone, but Moon and Chibimoon (especially Chibimoon) can grate on my nerves sometimes.
Now I want to watch the whole series again.