after years and years my pick still is When Marnie Was There. i listen to the playlist religiously
either the end of evangelion ost or the liz and the blue bird ost. both are absolutely spectacular, albeit in pretty different ways so it makes it kind of hard to compare the two.
it's not a movie, but I will never not sing the praises of IGPX's soundtrack—
IGPX
The music for the series was handled/contributed by Ninja Tune, an independent British record label known for electronica, IDM & hip-hop—making for a very unique sound to the show, unlike most any other I've seen
The music varies from cut-to-cut, but the broadcast/Toonami version has, hands-down, the sickest anime OST in my stinky opinion
it featured artists such as: (all entries have linked tunes that were used in the show)
• Amon Tobin
• The Cinematic Orchestra
• The Herbaliser
• MF DOOM as KING GEEDORAH
• Hint
• Diplo
• Coldcut
• Neotropic
• Jaga Jazzist
• Journeyman
• DJ Food
• Pest
• DJ Vadim
• Mr. Scruff
• Blockhead
• Hexstatic
—among many, many others
My favourite would be End of Evangelion by Shiro Sagisu.
Neon Genesis Evangelion The End of Evangelion
More recently Kevin Penkin's Made in Abyss: The Dawn of the Deep Soul is some of the best I've heard and also The Disappearance of Haruhi Suzumiya. Studio Ghibli films are simply blessed by Joe Hisaishi's work.