For the TOD, among people we know, I think BK is among the very best, but it seems that recently BK's work is starting to be more widely sung and appreciated.
Of course, I think Skip's work is not well-known enough - yet!
Among people we don't really know personally, I think Michael Stewart never really got his due in terms of reputation as a lyricist, but that may be because he only wrote lyrics for two hit shows, I Love My Wife and Barnum. i think Martin Charnin is undervalued as well, in terms of his overall body of work.