At the 2003 Laputa Animation Festival, held in Japan and named after the Studio Ghibli film Laputa: Castle in the Sky, 140 animators from around the world were asked what they thought were the greatest works of animation of all time. Their ballots were collated by the festival organizers and published in a limited edition booklet, and these are the results. (A very large number of these are available on YouTube and elsewhere online if you look.)

You can find this list in a few different places online. The most authoritative and informative place (and the site I depended on for this list) is at the Nishikata Film Review blog here: nishikataeiga.blogspot.com/2010/10/laputas-top-150-japanese-and-world.html

The results were not limited to feature films or short films, but could include any type of animation the animators polled wished to include. Consequently, there were several television series, several series of short films condensed into one spot, a credits sequence, a group of TV commercials, and a music video. The entries which Letterboxd did not include in its database are as follows:

60. Lupin III (1971 TV Series, dir. Masaaki Osumi/Hayao Miyazaki/Isao Takahata)
81. [TIE] Good Night Children (credits sequence for TV show, 2000, dir. Yuri Norstein)
127. [TIE] Rainbow Squadron Robin (TV series, 1966-1967, dir. Takeshi Tamiya)
133. [TIE] The Gutsy Frog (1972-74 TV Series, dir. Eiji Okabe, Tadao Nagahama)
133. [TIE] Yakult Miru Miru claymation commercials for probiotic drink (PMBB/Misseri Studios, ITALY/JAPAN, from 1980 on)
149. [TIE] music video for "Sledgehammer" by Peter Gabriel (1986, dir. Brothers Quay, Aardman, et al.)

Also, it should be noted that several of the entires on this list that I have put on here are really stand-ins for the actual films or series, and I merely went with what was available on the Letterboxd database.

So, #6 Mirai Shounen Conan appears to be a condensed video version of the 1978 TV series directed by Hayao Miyazaki. #31 The Adventures of Gamba also appears to be a film-length condensation of the 1975 TV series, though both are listed under director Osamu Dezaki. Likewise, #46. Neon Genesis Evangelion: Death and Rebirth stands in for the complete 26-episode TV series Neon Genesis Evangelion (1995-1996).

More confusingly, perhaps, #32: The Cat Concerto really stands for the entire Tom and Jerry series of short films directed by William Hanna and Joseph Barbera. I chose it because it seems to be the most acclaimed single short of the series.

Other cases where an individual film or a video collection is made to stand in for an entire series include the Astro Boy; The Brave in Space (for the original 1963 TV series), Mobile Suit Gundam 1 movie (for the original 1979 TV series), Snow White 1933 (for the entire Betty Boop series of shorts), Cheburashka (for the series of 4 shorts by Roman Kachanov), Heidi torna Sui monti video (for the complete 1974 TV series Heidi, Girl of the Alps), Superman: The Mad Scientist (for the whole series of Fleischer Superman shorts), Marco: 3000 Leagues in Search of Mother movie (for the complete 1976 TV series), Anne of Green Gables: Road to Green Gables (for the complete 1979 TV series), Steamboat Willie (for the complete series of Mickey Mouse shorts starting in 1928), Fast and Furry-ous (for the complete series of Chuck Jones shorts), Popeye the Sailor (for the complete series of Fleischer shorts), Panda! Go Panda! (for both 1972-73 short films), Space Battleship Yamato movie (for the original 1974-75 series), Ashita no Joe 2 movie (for the complete 1980-81 series), Study No. 1 (for all 13 "Study" shorts by Oskar Fischinger), the 8 Man video (for complete 1963-63 TV series), and Peter Gabriel--Play the Videos (for "Sledgehammer").