.

Man... I could take up a lot of space here detailing my many favorites from Giffen. I think his very best work was in 1982-1983, on LEGION OF SUPERHEROES 285-306
https://viewcomiconline.com/legion-of-super-heroes-1980-issue-285/

And on the "Doctor Fate" backup stories in FLASH 306-313 :
https://viewcomiconline.com/the-flash-v1-306/

The first few appearances of Ambush Bug, in DC COMICS PRESENTS 52 and 59, and in ACTION COMICS 560, 563 and 565 in 1982-1984 :
https://viewcomiconline.com/dc-comics-presents-v1-052/
https://viewcomiconline.com/action-comics-1938-issue-560/
https://viewcomiconline.com/action-comics-1938-issue-563/
https://viewcomiconline.com/action-comics-1938-issue-565/

Also the first 6 issues of OMEGA MEN :
https://viewcomiconline.com/the-omega-men-1983-issue-1/


And for me another high-point, the Giffen/DeMateiss run, with artists Kevin Maguire and then Adam Hughes, in JUSTICE LEAGUE 1-60 from 1987-1992, also expanding from JUSTICE LEAGUE (1-6) into JUSTICE LEAGUE INTERNATIONAL (issues 7-25), and then JUSTICE LEAGUE AMERICA (26-60).
And expanding from that series, there was also JUSTICE LEAGUE ANNUAL, and JUSTICE LEAGUE QUARTERLY.
And the hilarious spin-off JUSTICE LEAGUE EUROPE 1-36.
https://viewcomiconline.com/justice-league-1987-issue-1/ (issues 1-6)
https://viewcomiconline.com/justice-league-international-1987-issue-7/ (issues 7-25)
https://viewcomiconline.com/justice-league-america-issue-26/ (issues 26-60)
https://viewcomiconline.com/justice-league-europe-issue-1/ (1-36)


Plus Giffen work on many other series. Some of my favorites are Giffen's 1970's and early 1980's work, at both Marvel and DC. Such as :
AMAZING ADVENTURES 35 and 38 (both Killraven),
CHALLENGERS OF THE UNKNOWN 83-87
CLAW 8-12
DC COMICS PRESENTS 52 and 59
DEFENDERS 42-54
GHOSTS 104, 106 and 111
IRON MAN 114
KAMANDI 44-47
LEGION OF SUBSTITUTE HEROES SPECIAL
MARVEL PREMIERE 31 (Woodgod), and 44 (Jack of Hearts)

But I started the list with my absolute favorites, Giffen's LEGION and DOCTOR FATE work, and Ambush Bug.
Art-wise, that was Giffen at the peak of his talent. These are issues I pull out and re-read frequently.