When it comes to James Bond scores, you have to separate the soundtrack (the music that plays over the whole movie) and the title song (which plays over… Err, the titles).
James Bond soundtracks have had many different composers, with John Barry (who passed away in February 2011) and David Arnold the two composers who did the most. John Barry created the famous "Bond sound" with soundtracks to the early Bond films and his best soundtracks were Goldfinger and On Her Majesty's Secret Service, with The Living Daylights an exceptional score later in the series. David Arnold did most of Brosnan's Bonds and his best score was to Casino Royale.
My opinion: Goldfinger and Casino Royale are tied, with OHMSS coming in a close second.