For me there is no "worst" or "best" score. There is something good in all of the scores to find.
Overall if I must choose, I'd say TLD is the best and Skyfall is the worst.
Skyfall because it could be ANY common action movie score, nothing in there that identifies Bond.
And I am saying this as a fan of Thomas Newman in general.
Here is a list of some of my favourite tracks from the 24 soundtracks:
007-John Barry (FRWL & TB)
Capsule In Space-John Barry (YOLT)
OHMSS-John Barry (this is the best piece of instrumental music ever and even one of the best tracks ever and I absolutely LOVE the Propellerhead's version of it)
Bond Meets Solitaire-George Martin (LALD)
Bond77-Marvin Hamlisch (TSWLM)
The Palace Fight-John Barry (OP)
Snow Job-John Barry (AVTAK)
Necros Attacks-John Barry (TLD)
Ice Chase-John Barry (TLD)
The GoldenEye Overture - Eric Serra
Backseat Driver-Propellerheads (TND)
Come In 007, Your Time Is Up-David Arnold (TWINE)
Ice Bandits-David Arnold (TWINE)
Hovercraft Chase-David Arnold (DAD)
Night At The Opera-David Arnold (QOS)
Grand Bazaar Istanbul-Thomas Newman (SF)
Backfire-Thomas Newman (SP)
Furthermore I absolutely love:
Where Has Everybody's Gone & If There Was A Man-The Pretenders (TLD)
James Bond Theme-Moby (TND)
James Bond Theme-Paul Oakenfold (DAD)
Dalton Rulez™