I wasn't able to find the full list (you have to buy the guide I guess), but Zagat's most recent data indicates that west coast diners are the most stingy in the nation:
From
this press release:
Tipping: Among the nation's most generous tippers are Denver (19.5%),
Detroit and Philadelphia (19.4%), all exceeding Zagat's national average of
(19%). West coast diners in San Francisco and Los Angeles are among the
least generous at 18.4%, while Honolulu averages a desultory 18% tip.