MAC's Russian Red. I used to love Ruby Woo when I first discovered matte, retro lip colors, but it really does suck the softness out of my lips. Russian Red dries me out a bit, too, but it's such a true and gorgeous color. Doesn't clash with my yellow-toned skin, and behaves very well.
When I'm not doing a lined & defined "perfect red lip" (as in...sort of smudgy, maybe put some gloss on top, "I've been making out for hours" look) I can use almost any drugstore true red and it'll be fine.