People who've only watched the more recent ones will probably lean toward Onatop or Natalya. I like them too, but personally think some of the old school girls were the best/hottest. Tough to pick my single favorite, but I can narrow it down to 3 pretty quickly:
-Honey Ryder (Ursula Andress - set the standard)
-Domino (Claudine Auger - the hottest Bond girl ever IMO)
-Solitaire (Jane Seymour - probably the cutest Bond girl)
How anyone could pick Denise Richards as Christmas is beyond me. Different strokes I guess. Yes, she has a great body and was easy on the eyes in that wet t-shirt the last 10 minutes of the film, but her crappy acting (and this is a Bond film where mediocore acting is commonplace so that's saying a lot) pretty much ruined that film for me. One of the worst Bond girls since Magda in Octopussy.