Be interesting to compare the films by specific elements: Shrublands scenes, Nassau scenes, casino/dance with Domino, death of Largo, etc
I love both films, but overall clearly, TB is the classic Bond.
In TB the Schrublands scenes have that playful Connery/Molly Peters banter, the rack, a GREAT barry score and some overall fun moments.
By contrast, I probably like the Schrublands scenes in NSNA equally. I love the seduction of Prunella Gee, the fight with Lippe, Fatima's thrashing of Chuck Cunningham himself Gavin Oherilhy, and some of the jokes.
Thunderball is drenched in beautiful Nassau atmosphere and surroundings. The Bahamas in TB is as much a character in the film as Bond. NSNA on the other hand gets thru this location quickly and it's off to France. I do love the scenes in the Bahamas in NSNA, though, but I'd give TB the edge.
The sequence where 007 rides the boat to the casino is pure Bond in TB. The Chemin de fer sequence is a slight replay of the DR NO sequence, but has great has great interplay between Bond and Largo. I'd say the same with NSNA although the game is different and very 1983. As far as the dance, TB is far more romantic in tone whereas the tango is kind of funny in NSNA.
Largo's death follows the book more in NSNA, whereas the fight aboard the Disco Volante in TB is fun back projection notwithstanding.
I really do love both films. NSNA gets a lot of flack for not being an Eon Bond, but I certainly prefer it to many of the other Eons,