My rarest chameleons were the B. transvaalense that a few of us imported from Europe. I paid $500 for one. That's also the most I've paid for a chameleon, everyone else has never surpassed the $300 mark.
My most beautiful is hard to say. I find my panther cross, Daedalus, to be my long-term secret favorite but I find all of my Meller's chameleons stunning. My female is over the 550 gram mark and it's just awesome to see a chameleon that large living in my living room. And I just love the look of a nice, healthy Meller's, I love their color, their face, and their scalloped backs. The Meller's I've had have come from varying sources, from rescues to show purchases, and from free to $250 - most of them WC but one was CB.
My carpets had to be a close second on the beauty scale (F. Lateralis) but they were too small. I love big chameleons.